Boo

Boos (originally known as "Boo" Diddlys and later Boo Buddies   ) are common ghost enemies in the Mario franchise that first appear in Super Mario Bros. 3. They are a type of white, spherical ghost with menacing and normally open mouths. They are known for their large tongues and small "arms" of some sort. However, the most distinctive characteristic of the Boos is their shy personality, where they cover their faces when someone looks directly at them. They will uncover their faces once the subject turns around.

Super Mario Bros. 3
Boos first appear in Super Mario Bros. 3. Here, they are referred to as “Boo” Diddlys, a pun off the late rock star. However, future games refer to them only as Boos. They make their first appearance in. The Boo shields its face if Mario or Luigi look at it, but it starts to chase Mario or Luigi, faster than in succeeding games, if they look away. Boos are unable to be defeated unless the two are equipped with a Hammer Suit, Koopa shell, or Starman. The game also has Stretches, which are Boos with very long bodies that live in the Fortresses throughout the Mushroom World. In the original, depending on the level's palette, Boos have either a dark blue or dark red outline.

Super Mario World
In Super Mario World, Boos are now called "Boo" Buddies (though they were still called "Boo" Diddly earlier in development ) and they reside in the many Ghost Houses in the game. These Boos retain their usual pattern of attack from Super Mario Bros. 3 and sometimes make faces at Mario or Luigi. However, they are somewhat slower and less accurate than in Super Mario Bros. 3. This game also introduces many new Boo variations, such as the Boo Buddy Block, Boo Buddy Snake, Boo Crew, Circling Boo Buddies, Eeries, and Disappearing Boo Buddies. It also introduces a giant version of the Boo, the Big Boo. One Ghost House contains a secret boss, a special Big Boo. The only way to defeat a Boo is with Super Stars or with Grab Blocks when it is visible. Unlike later games, the Boos in this game seem to have multiple tails. The groups of Boos also have different facial expressions, while individual Boos change theirs for a brief second if left alone for a while.

Super Mario Land 2: 6 Golden Coins
Boos appear in Super Mario Land 2: 6 Golden Coins. These Boos are relatively unchanged from the previous Boos from Super Mario Bros. 3. Boos in this game are found in the Pumpkin Zone. A thrown Green Shell can defeat it. A variant named Terekuribō, which resemble ghostly Goombas, also appears in this game.

Super Mario 64 / Super Mario 64 DS
Boos (also called Baby Boos ) make a starring appearance in the course Big Boo's Haunt in Super Mario 64. A group of Boos can be found in the castle gardens (eight of which are holding Red Coins in the DS version). After collecting twelve Power Stars, Mario is able to enter Big Boo's Haunt by going into the little cage that a certain Boo drops; this Boo will be somewhat bigger than the others. He also battles Big Boo three times here. Additionally, when Mario looks at the Boos, they attempt to hide by becoming partially transparent, but if Mario is not looking at them, they chase him. If they hit him, he loses two wedges of health. In the translucent Boo, the player can see a coin or a Blue Coin. To defeat them, a punch or kick from behind or the side is needed. They can also be defeated with a Ground Pound while he is not looking at them. When defeated, they give a Blue Coin, but the ones in the castle gardens give a normal coin instead. When defeated in the first mission, Go on a Ghost Hunt, the Boos will say, "Ghosts... ...don't... ...DIE! Heh, heh, heh! Can you get out of here... ...alive?" when defeated. In addition, a Boo will appear in the hallway of the Mushroom Castle after twelve Stars are collected.

In Super Mario 64 DS, eight Stars are needed to spawn a small Boo in the hallway, who holds a Red Coin. After fifteen Stars are collected, the small Boo is replaced by a Big Boo, which then allows Mario to enter Big Boo's Haunt. Sometimes, if the player is not Luigi, one particular Boo will wear a Luigi Cap. In the haunt, Mario can find a Luigi painting, which will take him to the Big Boo Battle level on the balcony. After defeating King Boo within, Mario gains the key to the room in which Luigi is imprisoned and proceeds to free him. In the English version of the game, King Boo is incorrectly referred to as "Big Boo." Yoshi cannot defeat Boos in this game. Ground-pounding yields no results, and eating them simply causes Yoshi to spit them back out. Fortunately, Mario, Luigi, or Wario can hit Boos with Ground Pounds.

Super Mario Bros. Deluxe
While Boos do not appear in the original Super Mario Bros., Boos appear in Super Mario Bros. Deluxe as the main enemy in the "You VS. Boo" mode. The goal is to reach the flagpole before the Boo. After defeating Boo within a certain time frame, it flies away, and a Green Boo replaces it. After that Boo is defeated, a Red Boo takes its place, and finally, a Black Boo with a yellow outline appears. Each new Boo gets progressively faster than the one before it, meaning the plain White Boo is the slowest, while the Black Boo is the fastest; the Black Boo copies the player's best time, which makes it the hardest to defeat.

Super Mario Sunshine
Boos return in Super Mario Sunshine, terrorizing the residents of Hotel Delfino. In this game, they move around in slow, swooping motions and do not care if Mario looks at them. They tend to go in Mario's general direction while turning invisible (aside from some distortion), but spraying them with F.L.U.D.D. causes them to slowly become visible again. These Boos can be defeated by being jumped on, making Super Mario Sunshine the only game outside of the Mario RPGs where jumping can defeat them. Boos in this game can also be eaten by Yoshi. They also disguise themselves as Yellow Coins and Blue Coins, which unlike the real ones do not spin. Boos can also disguise themselves as Shadow Mario while the real Shadow Mario runs from Mario, though they appear lighter than Shadow Mario, lack the Magic Paintbrush, and do not have the theme music. When Mario approaches a disguised Boo, it laughs and bumps into him, though if it is sprayed beforehand it will start behaving like the other Boos. Like the other enemies, Boo's design is changed for this game, with drooping eyelids, blue circles surrounding their black pupils, and long, coiled tails. This is due to the fact that they are made from graffiti.

The Boos in this game are led by King Boo. Mario finds him in the basement of the hotel's Casino, and he has to battle him. He can defeat him by throwing a Chili Pepper at him and then throwing another piece of fruit at him. Mario has to do this three times before King Boo is defeated. Pink Boos also appear and can be turned into a platform if sprayed by F.L.U.D.D. Also appearing inside the hotel are a new species, known as Sleepy Boos. These Boos mostly appear to block passages. F.L.U.D.D.'s water does not affect them; they can be removed only by being eaten by Yoshi.

New Super Mario Bros.
Boos also appear in New Super Mario Bros.. They are found mainly in Ghost Houses scattered throughout the game, as well as World 8-1. They appear like they usually do, shy, and they act the same as in Super Mario Bros. 3. They can only be defeated with a Shell, a Starman, a Mega Mushroom, or a Blue Shell. The game also introduces the Balloon Boo, which are normal Boos who can suck up air, and become much bigger. Broozer, the boxing ghost, first appears in this game as well. An icon of 2 Boos covers the progress map in Ghost Houses.

Super Mario Galaxy
Boos make an appearance in Super Mario Galaxy and can be found in the Ghostly Galaxy, the Bigmouth Galaxy, the Deep Dark Galaxy, and the Sand Spiral Galaxy. Boos act the same way that they did in previous games, such as hiding by turning transparent when Mario looks at them and then following Mario when he looks away. Boos can be defeated only when they are brought under a ray of light (including the Toad Brigade captain's helmet and the light emitted from shells while in the water) or by Rainbow Mario touching them. The spin attack, however, can throw a Boo around Mario, knocking it off course temporarily or into a light. Boos can also be found underwater in the Bigmouth Galaxy where they attack just by swimming back and forth, similar to Cheep Cheeps. In Deep Dark Galaxy, in the secret mission, there is a large Boo that has a Power Star in it.

Boo Mario also appears in this game. Mario has the same body as the other Boos, but retains his face when in his Boo form. He also wears his trademark cap on his head. If a Boo spots Mario while he is a Boo, it develops an attraction for him and follows him. If a Boo hits Mario, Mario loses the powerup but does not lose any health.

An individual Boo named Spooky Speedster is found in two areas of the game. Mario must race him twice to win a Power Star; once in the Ghostly Galaxy and once again in the Boo's Boneyard Galaxy. This game also introduces a new kind of Boo, called the Bomb Boo; it is similar to a normal Boo, but is black with yellow eyes and can be grabbed by its tongue if Mario uses his spin attack on it.

Captain Toad also indirectly suggests that Boos eat people, as he worried that Luigi might have been eaten by ghosts.

New Super Mario Bros. Wii
Boos reappear in New Super Mario Bros. Wii in Ghost Houses throughout the game. They behave the same way as they did in New Super Mario Bros. and are invincible, unless the player has a Star power-up. Big Boos also reappear along with Broozers. Circling Boo Buddies can also be found in a small number of Ghost Houses in the game. Despite their concept art, they appear with a blue glow as opposed to plain white in this game, giving off a more spectral appearance. In the level selection screen, a single Boo will be watching Mario and will taunt Mario as he enters. If Mario gets tossed out, the Boo will laugh. However, once the level is beaten, the Boo will cover its face for the rest of the game.

Super Mario Galaxy 2
Boos reappear in the game Super Mario Galaxy 2. They behave the same way they did in its predecessor. They are found in haunted levels such as Haunty Halls Galaxy and Boo Moon Galaxy. The underwater Boos from the predecessor also appear in this game, in the Battle Belt Galaxy and Slimy Spring Galaxy. Bomb Boos and Mega Boos also reappear. A variant named Octoboo, which resemble ghostly Octoombas, also appears in this game.

Super Mario 3D Land
Boos later appear in Super Mario 3D Land. In the game, they retain their normal battle strategy, which is chasing Mario when he looks away while sticking their tongue out. Boos in this game also momentarily disappear when hit with Fire Mario's fireballs and Tanooki Mario's tail whips. Boos also laugh in their original phonic from Super Mario 64. Some Boos have striped tails; these are called Tail Boos. They act like normal Boos, but when they stop moving when Mario looks at them, they will swing their tails once, which can damage Mario. Big Boos also appear during the game. Another species of Boo is also introduced, called Peepas. They do not move freely like normal Boos and instead move around a set position, and do not halt when Mario looks at them, as in Super Mario Galaxy.

New Super Mario Bros. 2
Boos, along with Big Boos, return in New Super Mario Bros. 2, with the same appearance and behavior as in New Super Mario Bros. Wii, except they turn completely red when Mario faces them. They can be found in Ghost Houses along with other ghost enemies such as Peepas and the new Boohemoth. All of these varieties, save for Boohemoth, can be defeated with a Star or Gold Flower. Boos can also be turned Gold Boos with a Gold Ring. When gold, Boos float away from Mario, leaving a trail of coins behind them.

There are also Boos that push walls in a Ghost House, namely World 4's Ghost House. Here they push the wall either left or right and they do not stop when Mario looks at them.

New Super Mario Bros. U
Boos, Big Boos, and Circling Boo Buddies appear in the Wii U title New Super Mario Bros. U. Their behavior is the same as that of past installments. Boos also have their own Enemy Course in the haunted area of the Soda Jungle, where a group of Boos appear in an area with various Donut Blocks, and defeating them must be done using the Super Star located inside a Flying ? Block. They can also be defeated with a Baby Yoshi.

Super Mario 3D World / Super Mario 3D World + Bowser's Fury
Boos appear in Super Mario 3D World and Super Mario 3D World + Bowser's Fury, along with Peepas and Big Boos. They retain the same strategy from Super Mario 3D Land and utter the same laugh from Super Mario 64. They appear to be a bit more transparent than in previous mainstream Mario games and give out a blueish glow like in the New Super Mario Bros. games, as well as a reddish glow and even steam when Mario faces them.

Super Mario Maker / Super Mario Maker for Nintendo 3DS / Super Mario Maker 2
Boos reappear in Super Mario Maker, Super Mario Maker for Nintendo 3DS, and Super Mario Maker 2 as enemies. They function the same as previous games. In the Course Maker, they can be placed as enemies and can be shaken to turn into Boo Buddies. They can also be dragged onto a platform, turning them into Stretches. Like many enemies, they can be enlarged by a Super Mushroom and be given wings. The former will turn it into a Big Boo, and the latter will make them move much faster. They can be placed in Warp Pipes, Bill Blasters, Blocks, and tracks. In addition, adding Wings to a Boo Buddy makes the Boo Buddy move in and out. If a Boo is placed in a Koopa Clown Car, the Koopa Clown Car stops and closes its eyes when it is looked at, and sneaks up on the player when looking away.

Super Mario Run
Boos appear in Super Mario Run in Ghost House levels. When Mario looks at them, they cover their eyes and float up and down. They attack Mario by quickly following behind him. Mario can defeat them by backflipping over them. In some levels, pressing the pink P Switch defeats Boos on-screen. They can drop Keys, Coins, or Color coins after they are defeated, and the object they contain inside of them can slightly be seen through them before they are defeated. In Dark and Stormy, Boos are defeated when a lightning strike occurs. Stretches also appear in the game.

Super Mario Odyssey
Boos do not appear physically in Super Mario Odyssey, making this game the first Super Mario game to not contain Boos since Super Mario Land. However, Peach wears a Boo mask on the side of her head when she visits Bowser's Kingdom, a common way to wear masks of  in festivals in Japan.

The Adventures of Super Mario Bros. 3
Boos make infrequent appearances in The Adventures of Super Mario Bros. 3 television series, which depicts them as having a somewhat menacing appearance. They are depicted with red eyes and yellow teeth. Like in the game the show is based on, Boos work for Bowser and often aid him in causing trouble. An example of this is seen in the episode "Reign Storm," in which Bowser has several Boos terrorize the new Mushroom Shopping Mall. In this episode, they are referred to as "Boo Diddlys."

Super Mario World television series
In Super Mario World, Boos, who are completely redesigned, appear in the episodes "Ghosts 'R' Us," in which a gang of Boos, as well as a Big Boo, appears to chase Yoshi through Wizenheimer's haunted house; "The Night Before Cave Christmas," in which they scare Yoshi away; and "The Yoshi Shuffle," in which several Boos appear in the audience during the episode. They are never referred to by name, instead simply being referred to as "ghosts." They more closely resemble their in-game sprite.

Nintendo Adventure Books
In Koopa Capers, a Boo confronts Luigi if he decides to simply look through a keyhole in a fortress door, instead of barging through it. If Luigi decides to run away from it immediately, he will successfully escape, but if he decides to stand his ground, the Boo will chase him onto some floating blocks after he dodges its attack. Making a beeline for the door after mounting the blocks will allow the Boo to catch Luigi, but doing evasive techniques will allow him to escape it. When he begins his descent into the Magma Pit, Luigi will hear a Boo behind him, which causes him to pick up the pace, and escape it.

Illustrations of a Boo are used in puzzles in Dinosaur Dilemma and Flown the Koopa, though none appear in the actual stories.

Super Mario World: Mario to Yoshi no Bōken Land
In the interactive OVA Super Mario World: Mario to Yoshi no Bōken Land, Boos appear in a Ghost House that Mario, Luigi, and Yoshi are passing through. A Boo starts following Luigi, who is in the back, but every time he turns around, it disappears. Finally, he quickly does a double take, and turns just in time to see it re-materialize. He panics and Boos start swarming the group. Mario grabs a candle and lights it, which repels the Boos, and one drops a key they need to progress.

Yoshi
Boo Buddies make an appearance as one of the six falling objects in Yoshi. Boo Buddy's sprite in this game is similar to its sprite from Super Mario World.

Yoshi's Cookie
In Yoshi's Cookie, Boos return as enemies to Yoshi. Though in this game, they are depicted as one of Yoshi's "opponents". They are among the easy opponents, the others being Goomba, Cheep Cheep, Paratroopa, and Spiny. Eeries also appear, as well as the similarly-named Fishin' Boos.

Yoshi's Safari
Boos (misnamed "Big Boo" in the English manual ) appear as enemies in Yoshi's Safari. Their first and only appearance throughout the game is in Ghost Mansion, a level in the Dark Realm. Unlike most enemies in the game that can be shot with the Super Scope to be defeated, shooting a Boo stops it in its tracks. While stunned, Yoshi can then run into it to defeat it. Defeating a Boo adds 500 points to the player's score (1,000 in Hard Mode), the highest amount of points earned from regular enemies. A Big Boo serves as the boss for the level.

Super Mario World 2: Yoshi's Island
Boos also appear in Super Mario World 2: Yoshi's Island and its remake Yoshi's Island: Super Mario Advance 3, where they are depicted with happy faces. They are first seen in World 2, which features numerous ghastly creatures. The only way to defeat Boos is by looking away and then make an egg bounce off a wall after it is thrown, hitting the ghost in the face. Kamek the Magikoopa turns one Big Boo into Bigger Boo, which serves as a mini boss and grows in size every time he is hit by an egg. The main boss of World 2 is also a Boo-like creature, Roger the Potted Ghost, who was a normal flower pot until Kamek made him giant and transformed it into a living creature. The game also features the Boo Balloon, who are balloons made to look like Boos that yield items when they pop, as well as Boo Man Bluff, a blindfolded Boo that relies on noise to detect the player.

Yoshi's Story
Boos appear in Yoshi's Story in Stage 6-3: Ghost Castle. They do not act differently, although they are slightly bigger. The Ghost Castle is also home to other Boo species: namely, the Boo Block, Blindfold Boo, and Little Boos. Another variant, the Jelly Ghost, inhabits the jelly of Stage 2-3: Jelly Pipe and Stage 2-4: Torrential Maze. The Big & Little Boo family also appears in Jelly Pipe.

The normal Boo is mistakenly called a Big Boo in the Nintendo Power guide.

Yoshi Topsy-Turvy
Boos appear again in Yoshi Topsy-Turvy. In this game, they only appear in mission 6-7, with Big Boos being more common. They follow the same tactics as normal and are given their laugh from preceding releases.

Yoshi's Island DS
Yoshi comes into contact with Boos, again, in Yoshi's Island DS. Here, they are commonly found in castles, along with other ghastly creatures. Again, they work for Kamek. They attack the same as all Boos before, but like in Super Mario World 2: Yoshi's Island, they can only be defeated if Yoshi looks away. So Yoshi must bounce an egg off of the wall into their face to defeat them. A Boo-like mid-boss named Hector the Reflector appears as well. The Boos' laughs are used in many games before. It is used for the boss Six-Face Sal, and even Baby Bowser. Their artwork depicts them like in the main series, but the in-game sprites are based on Super Mario World 2: Yoshi's Island's.

Yoshi's New Island
Boos return in Yoshi's New Island, and act the same way as in past games. They first appear in World 2-4: Beware the Boo Brigade. Big Boos also appear.

Super Mario Kart
Boos made their first appearance in the Mario Kart series in Super Mario Kart as items exclusive to "2 Player" mode, under the name "Ghosts". When the player uses it, they will become transparent temporarily (19 seconds), while the "Ghost" steals the opposing player's item, if available. They also appear as background elements in the three Ghost Valley courses, where they laugh when the player drives by.

Mario Kart 64
Boos (or Ghost Bonuses ) return as a usable item in Mario Kart 64. They can be obtained if the player is in the top two positions. When activated, the Boo selects a racer with the best item in reach, steals the item, and gives it to the player that released it. At the same time, the player obtains total invisibility and invincibility for a short period of time. While invisible, the player can pass the items, the course obstacles, and the other racers more easily by simply going through them. If no other players possess items, the Boo will return empty-handed. Boos also appear in Banshee Boardwalk and the image of one appears in neon lights in Rainbow Road, both as background elements.

Mario Kart: Super Circuit
Boos appear as items again in Mario Kart: Super Circuit. When activated, they can also slow down the leading racer. Starting in this game, if a CPU racer uses a Boo, it can also steal items from the player and make the player lose Coins. The transparency effect lasts for five seconds.

Boos also appear in two new courses, Boo Lake and Broken Pier. At Boo Lake, Boos hold candles that guide the player through the track. On Broken Pier, they attack the players and take their Coins.

Mario Kart: Double Dash!!
Boos do not appear as items in Mario Kart: Double Dash!!. However, Boos, as well as the Boolossus' gold frame portrait, appear in the Luigi's Mansion battle course. Also, King Boo makes his Mario Kart debut as a playable character.

Mario Kart Arcade GP
Boos appear as items in the arcade game, Mario Kart Arcade GP. A Boo appears as a basic item. It causes whoever is hit by it to slow down temporarily. There is also a new item called the Triple Boo.

Mario Kart DS
In Mario Kart DS, Boos reappear as items (with the name of Boo Hoo in the European instruction manual ). They can be obtained if the player is anywhere from 3rd to 7th place. The only differences are, they do not slow down the leading racer, and they no longer steal the best item in reach. Instead, they just steal the nearest racer's item. Additionally, while using the Boo item, the player will not be slowed down while driving on off-road surfaces, allowing various shortcuts to be made. Some pictures of Boos from the game, Luigi's Mansion, appear in the Luigi's Mansion race course. Banshee Boardwalk reappears as a race, along with the Boos. They do not do anything that affects the racer; they just laugh when a racer drives by.

Mario Kart Arcade GP 2
Boos reappear in the arcade game, Mario Kart Arcade GP 2. Like what they do in Mario Kart Arcade GP, they slow down the leading racer. Though, the Triple Boos do not appear in this game, even though it appears in the predecessor.

Mario Kart Wii
Much like in Mario Kart: Double Dash!!, Boos do not appear as items in Mario Kart Wii, but King Boo appears as a playable character. However, Boos do appear in a returning course, Ghost Valley 2. Like their original appearance in the track, Boos only laugh when racers drive by, but they eventually disappear. Boo also makes a cameo in Bowser's Castle. At the end of the track, Boo's Mario Party 7 artwork can be seen along with Dry Bones' artwork.

Mario Kart 7
In Mario Kart 7, Boos appear in the returning track, Luigi's Mansion, in place of the portrait ghosts. They will pop out of their paintings when the drivers race by them. They also appear as spectators on Toad Circuit.

Mario Kart Arcade GP DX
In Mario Kart Arcade GP DX, Boos return from Mario Kart Arcade GP 2 as items.

Mario Kart 8 / Mario Kart 8 Deluxe
In Mario Kart 8, Boos appear as obstacles on Twisted Mansion. If aimed correctly, the players can land on the Boos floating around near the gliding section. They also possess Hammer Knights near the end of the track.

In Mario Kart 8 Deluxe, King Boo is again a playable character, and Boos can also be seen floating around on. Boos also appear as items again, acting as they do in Mario Kart DS, though the mechanics are slightly different. Unlike in that game, Boo users are still slowed down by off-road surfaces. Boos immediately steal an item from a random racer in front of the user, and invincible or other invisible players are not immune; the Boo will bring back a Mushroom if there is nothing to steal. The Boo is visible, both when it steals an item and when it gives the stolen item to the user. It takes a couple more seconds to deliver the item back to the player, however. Only one Boo can be in play at a time; once it brings back an item, another can appear in item boxes again, even while another player is still invisible. Lastly, due to the way deployed items work, a Boo is able to steal any timed or multiple usage item, except for a Crazy Eight, or a Potted Piranha Plant and Bullet Bill already in use. Doing so will always give the user a fresh version of the item.

Mario Kart Tour
Boos reappear in Mario Kart Tour in the courses DS Luigi's Mansion and SNES Ghost Valley, where they act the same as they did on those courses in previous games. In both courses, wooden cutouts of Boos appear.

During the 2020 Halloween Tour, jack-o'-lanterns are scattered throughout the courses. Some jack-o-lanterns have Boo faces.

Mario Kart Live: Home Circuit
Boos reappear in Mario Kart Live: Home Circuit in Boo Fortress, frightening racers who hit them.

Super Mario Adventures
In Super Mario Adventures, a horde of Boos appear to attack Mario and Luigi when they are tricked into a haunted house by Bowser and the Koopalings. Mario and Luigi become trapped by the Boos and a Big Boo, who are held at bay by the bros staring at them in the face. Eventually, nearing exhaustion, Mario races to a nearby room, dragging Luigi while being chased by the Boos. Upon barging into this room, the Boos and Big Boo find Mario dressed as a psychiatrist with Luigi as his nurse. After some talking, Mario and Luigi manage to reform the Boos and the Big Boo, while learning they were bullied in their youth (which is why they act so nasty to everyone). These Boos and their Big Boo leader were last seen happily waving goodbye to Mario, Luigi and Yoshi as they left the haunted house, which the Boos led them out of.

Boos also make an appearance at Peach's wedding.

Mario Bros.
Boos make an appearance in the Super Mario All-Stars remake of Mario Bros., where they replace the Fireballs in the Battle Game found in the main menu of Super Mario Bros. 3 but not in the 2 Player Game's battle mode.

Hotel Mario
Boos also appear in the game Hotel Mario under the name Boo Buddies. There are two types of Boos in this game. One type stays visible but does not hurt Mario until it turns transparent. The other type of Boo uses the traditional attack method and turns invisible when looked at, and attacks Mario when his back is turned.

Mario's Picross
Boos also make a cameo appearance in the Game Boy game, Mario's Picross. They appear in one of the pictures in the "Early Picross" stage in level 6C. The other character that appears in the "Early Picross" stage is Mario, who appears in level 6H. Like their first appearance, Super Mario Bros. 3, they appear under the name Boo Diddly.

Mario Clash
Boos (misnamed "Big Boo" in the English manual ) make appearances in the Virtual Boy game, Mario Clash, where they are among the target enemies. In this game, Mario is able to attack a Boo from the side. Boos can become transparent by becoming dark like the screen, which causes them to become invulnerable, with shells simply passing through. For some reason, the English manual also refers to the Boos using feminine pronouns, similar to Cheep Cheep in the original Super Mario Bros.

Super Mario RPG: Legend of the Seven Stars
Boos return during the events of Super Mario RPG: Legend of the Seven Stars. The English translation erroneously calls them "The Big Boo". In the Japanese version in fact they are just called Teresa. These Boos, like other Boos that appear in previous games, hide behind their arms when stared at. However, some of The Big Boos teleport around the room, attempting to scare Mario and his friends. The Big Boos live in Kero Sewers along with many other ghouls, including Hobgoblins and Shadows. Often, these three undead monsters will assist each other in battle. Big Boos have no physical defense, making them extremely weak enemies (even a Goomba has three defense points). However, The Big Boos make up for their lack of defense with high evasion, meaning that most attacks against a Big Boo will miss. In battle, The Big Boos command powerful lightning magic, including the attacks Lightning Orb and Bolt. The Big Boos also know the special attack Scream, which cuts a party member's attack and defense in half. When not using magic, a Big Boo will approach one of Mario's party members and make a face, damaging that character. In this game, there is also a stronger Boo variation called Li'l Boos, which are the same size as normal Boos but have blue tongues, similar to the first appearance of King Boo. The only true appearance of a Big Boo in this game is the one used in Bowser's Terrorize attack. One The Big Boo lives in Monstro Town as part of the 3 Musty Fears.

Super Mario-Kun
Boos make appearances in some of the Super Mario-Kun comics. A Boo appears on the cover of the sixteenth issue. This issue is based on Super Mario 64. Alongside it, Eyerok, a Bob-omb, and Bowser can be seen. Throughout the comic, they appear, too. Their role in the comic is similar to their role in the game, where they are enemies to Mario and attempt to attack him. Lady Bow, a notable Boo, appears in a couple of the Paper Mario based issues. These issues are 25 and 27. Lady Bow appears on the cover of the twenty-fifth issue along with many of Mario's other partners, including Goombario, Kooper, Eldstar, and Twink. Besides appearing on the cover, she appears throughout the comic. Her role in the comic mimics her role in the game. Lady Bow reappears on the cover of the twenty-seventh issue and in the comic. Like in issue 25, Lady Bow's role in the comic is similar to her appearance in the game, where she helps Mario. In a Super Mario Galaxy based issue, Boo Mario appears on the cover along with more of Mario's transformations.

Game & Watch Gallery 2
Boos (called "Boo Buddies") appear in the Modern version of Vermin in Game & Watch Gallery 2. When Yoshi looks in the general direction of them, they refuse to move. When Yoshi looks away, they move towards the eggs. They only appear in groups of two or just one.

Game & Watch Gallery 4
A Boo appears in the Modern versions of Donkey Kong 3, Mario's Cement Factory, and Boxing in Game & Watch Gallery 4. In Donkey Kong 3, if Mario or Donkey Kong turns his back, it will slowly come closer to the player that it is closer to. If it gets close enough, the Boo will either scare Donkey Kong and award the player points (single-player mode only) or scare Mario and give the player a miss. In Mario's Cement Factory, a Boo will fly into the two containers on the second floor, clogging them up. The player does not receive any points for removing the Boo. In Boxing, one of the opponents Luigi faces is a Big Boo, who uses a regular Boo as a boxing glove.

Mario Party series
Boo has been a major character in the Mario Party series, from being a thief for hire to being a playable character.

Mario Party
Boos make minor appearances in Mario Party. Their voices can be mimicked by one of the items: the Talking Parrot. Boos also appear in each of the game's board maps, excluding Peach's Birthday Cake. On the boards, they steal Coins or Stars from opponents, and they are willing to steal a few coins for free from any player, although they will steal the number of coins at random. They also ask for 50 coins to steal a Star. If the player tells Boo that they do not want to steal anything, Boo will say "Don't feel so guilty. Ha ha ha!" Additionally, after the Luigi's Engine Room board is completed, a Boo, Koopa, and a Toad, along with the two runner-ups, surround the victor and congratulate them. Boos also appear in several mini-games, including Pedal Power and Running of the Bulb, and as one of the shapes the player can cut in the minigame, Crazy Cutter.

Mario Party 2
Boos make several appearances in Mario Party 2. In it, they steal Coins or Stars as they did in the first game. However, Boo charges 5 coins to steal coins instead of a free steal; and steals much more than in the first game. Additionally, an item called the Boo Bell appears. When a player obtains it, they can ring for a Boo to come. The Boo that comes to the player's side is asked to steal Coins or Stars, depending on how much the player can afford. If the Boo is sent to steal Coins from an opponent, the opponent can fight it off by pressing the A button quickly. Additionally, the Boo can only steal a maximum of 30 coins or a maximum of one Star.

A Boo also appears in the battle minigame Day at the Races along with the other racers; Whomp, Thwomp, and Bob-omb. The Boo can disappear and then reappear in a further spot on the racetrack. However, it gets its face stuck in the ground sometimes, causing it to stop for a short period of time.

Mario Party 3
Boos also appear in Mario Party 3. Like in their previous appearances, they are not major characters in the game. They are among the Duel Partners in the Duel Mode Partners. It is Yoshi's default partner, and when an opponent attacks, Boo can counterattack for equal damage, unless it was defeated by a Thwomp. Boo's attack is two, its health is one, and its salary is three coins.

Boos also appear in the unlockable party board, Waluigi's Island. Whenever a player runs into a Boo, it shows them two paths. One of the paths is rigged. If the player chooses the rigged path, they are sent back to the start. If they choose the correct path, they continue on the board. In addition, Boos appear on all of the other boards, Chilly Waters, Deep Bloober Sea, Spiny Desert, Woody Woods, and Creepy Cavern, serving the same function as in the previous games. On the board map, a picture of them can be seen next to a grave. They also return with the Boo Bell. Boos are also in the minigames Curtain Call, Stacked Deck, Three Door Monty, and Crowd Cover. Two portraits of a Boo can also be seen in Locked Out.

Mario Party 4
In Mario Party 4, a Boo plays a major role as the host for Boo's Haunted Bash. This is the first game where Boos use their modern design. This Boo wears a wizard's hat and cape, and like the other hosts in the game, it is the character to reward the player with a Star. Multiple Boos also appear on this board as background characters. A particularly surly one controls the Item Shop. Another one owns the Mystery Train, but it only gives out rides to the Boneyard if a Red Boo is not in its presence. Two side games involving Boos require a Mini Mushroom. One of them has the player pressing one of the keys of the Horn of Plenty to get one of three randomly chosen items. The second one has the character on a piano. They have to press the correct key at the right time until the end of the side game to get a certain amount of Coins. A question mark space activates a Boo clock. If three people land on them, Big Boo will appear. Big Boo is basically an upgraded version of the Boo House; he targets all players instead of one. The caped Boo is also the fourth host of the Reversal of Fortune, who oversees what is given.

Boos also appear on every other board in the game, stealing coins and Stars for the player at a shop called the Boo House in the same manner as Boos' previous appearances in the Mario Party series.

Also, a Boo is an unlockable, playable character in the Extra minigame, Beach Volley Folley.

In Long Claw of the Law, a Boo is one of the possible characters that needs to be collected.

Mario Party 5
Mario Party 5 marks the first game in the Mario Party series where Boo is a playable character in Party Mode. He is one of the new characters, the others being Koopa Kid and Toad. Boo's partner in the game is Koopa Kid. Since Boo is playable, he does not make any major background appearances. His previous role on the boards is now fulfilled by Chain Chomp.

Mario Party 6
A Boo reappears as a playable character in Mario Party 6. In the game, there is also an orb called Boo Away Orb, which protects the player from a Red Boo. Red Boos also appear in the minigame Boo'd Off the Stage and Boonanza!. Red Boos also appear on two boards, Towering Treetop and Castaway Bay where they let players steal coins and stars from others at night, similar to the Boo House in Mario Party 4. This game also marks the third appearance of Red Boos in the Mario Party series.

Mario Party Advance
Boos appear in Mario Party Advance as supporting characters. They appear in a few minigames, including Boo-Bye. In this minigame, regular Boos appear alongside Red Boos and Blue Boos. They also appear in Spooky Spike, in which one Boo serves volleyballs to the player, Floor It!, in which Boos are one of the possible passengers that must be brought to their respective floor, and Porta-Gust, in which the player can suck up Boos into a vacuum.

One of them, Boo, appears alongside some other Boos in the Boo Cemetery, where they are main characters in the quest True-Blue Boo.

Mario Party 7
Mario Party 7 marks the third Mario Party game where Boo is playable. It also marks Dry Bones' first playable appearance, who is Boo's partner throughout the game. Red Boos appear in the game, too. Red Boos appear in a few minigames such as Ghost in the Hall. In this minigame, Red Boos try to scare the players. Oddly, the Red Boos also try to scare Boo, if Boo is one of the characters. Boo shares the same special orb with Dry Bones, the Magic Orb. It allows them to double their dice roll during the next two turns and turns them invisible, making them immune to traps.

Mario Party 8
In Mario Party 8, Boo is a playable character for the fourth time in the Mario Party series. Boo's partner is Dry Bones, again. Red Boos appear in some minigames such as Boo-ting Gallery. Mario Party 8 also marks the first appearance of King Boo, who is the board host of King Boo's Haunted Hideaway. In order to get a Star, the player must find the room King Boo is hiding in and give him ten coins. There are three rooms, two of which contain a trap hole. If the player finds one of these rooms, several Red Boos will throw them in, forcing the player to start back at the beginning. When the player gets a Star, King Boo will rearrange the mansion's rooms. Red Boos appear as owners of the item shops.

Mario Party DS
Boo is not a playable character in Mario Party DS and plays no part in board play, but appears as an unlockable figure. They also appear in the minigames Boo Tag, and Peek-a-Boo. In Boo Tag, a Boo tags a player. The tagged player must try to get rid of the Boo by running into another player. The player that spent the least amount of time with the Boo wins. In Peek-a-Boo, the players must find the wanted Boo. A lot of different Boos appear in outfits, such as hats. Several of the wanted Boo appear, and once they are all gone, the game is over. The team that won the most Boos wins.

Mario Party 9
Boo does not return as a playable character in Mario Party 9, however King Boo is the boss of Boo's Horror Castle. Normal Boos also appear on the board. When the player passes a Boo portrait, a Boo will emerge and chase after the player. These Boos will move three spaces after each turn, and if a Boo catches up to the players (or vice versa), the current captain will lose half of all of their Mini Stars.

During King Boo's Puzzle Attack, whenever King Boo's health is depleted halfway, he sends Boos to attack the player. If the player's cursor touches a Boo, they are temporarily stunned. King Boo only sends one Boo at a time.

Mario Party: Island Tour
Boo returns as a playable character in Mario Party: Island Tour. This is the fifth time that Boo is playable, the first time he is playable on a handheld Mario Party game, and he is the first character in the series to be removed as a playable character in a main installment of the series and then return in a later installment.

Mario Party 10
Boo reappears in Mario Party 10 as a non-playable character. Whenever the player reaches a certain spot in the board Haunted Trail, Boo appears and steals five Mini Stars from a specific player for an indefinite number of turns. Boo will continue to harass the player until passed off to another player via a Boo Space or driven towards a Streetlight. Boos also appear in the minigame Boo Burglars, as enemies the players must examine, and appear as a balloon in the minigame Balloon Blast Bash. Several Boos also make cameos in the Luigi Board.

Mario Party: Star Rush
In Mario Party: Star Rush Boo has a special mode called Boo's Block Party. Players can participate in a single-player endless mode for a high score or compete in a one-on-one versus mode. When a player uses the Boo amiibo in Boo's Block Party, four Boos appear in the background; two on the top screen, two on the Touch Screen. If a player taps the Boo amiibo in the Mario Shuffle mode, the player can use Boo in that mode. They also appear in the Haunted Hallways and House of Boos minigames.

Mario Party: The Top 100
In Mario Party: The Top 100, Boo appears in minigames such as Slot Trot from Mario Party 6 and Jigsaw Jumble from Mario Party 9. However, in Minigame Match, Boo appears as an item via Boo Bell.

Super Mario Party
Boo returns as a playable character in Super Mario Party, which is his sixth playable appearance in the Mario Party series. Because of his status as a playable character, Lakitu takes his role as the one who steals coins or Stars from the earlier Mario Party installments. His Boo Dice Block consists of two of each -2 coins, 5, and 7.

Mario Party Superstars
Boo returns as a non-playable character in Mario Party Superstars, behaving like he does in the first three Mario Party games.

Mario Golf series
Boos make a couple of appearances in the Mario Golf series. In Mario Golf and in Mario Golf: Toadstool Tour a Boo appears in the top right corner of the screen to indicate the speed and direction of the wind.

Mario Golf
In Mario Golf for the Nintendo 64, Boos show where the wind blows by facing its direction in relation to the camera angle. They do not appear if there is no wind. Hole 2 of Mario's Star is designed after Boos. Also, Boos appear in the artwork for one of the courses, Boo Valley.

Mario Golf: Toadstool Tour
Boo is one of the unlockable characters in Mario Golf: Toadstool Tour, the others being Bowser Jr., Shadow Mario, and Petey Piranha, and is the only unlockable character in this game that appeared in the opening clip. In Bowser Badlands, Boos affect the trajectory of balls hit through them. Boos once again reprise their role of showing the wind direction, but they have another role; if a player delays in starting their swing, then two Boos carry a sign and float across the screen. These signs describe basic gameplay tips, but some are taunts to the player.

Mario Golf: World Tour
Boo returns in Mario Golf: World Tour as a playable character, this time being available from the start. Boos also appear in Hole 4 of Bowser's Castle floating in the sky alongside King Boo. For this installment, a "blowing cloud" is used instead of a Boo to indicate wind speed and direction.

Mario Golf: Super Rush
A Boo appears as a spin-type playable character in Mario Golf: Super Rush. Boo's special shot is Mischief Twister, in which multiple Boos appear and merge into Boo's golf ball before the swing for the shot is made. If it lands near other balls, Boos will come out and haunt them.

Mario Tennis (Nintendo 64)
Boo appears in Mario Tennis for the Nintendo 64, marking his first playable role. He is classified as a tricky character, the only other character of this class being Paratroopa. He is also a default character. Most of the playable characters have courts named after them. However, Boo does not have his own court.

Mario Tennis (Game Boy Color)
A Boo makes a cameo appearance in Mario Tennis for the Game Boy Color. They can be seen in the audience at Peach's Castle.

Mario Power Tennis
Boo also appears in Mario Power Tennis where it is a playable character. When it wins a championship, Mario and Luigi would come out with the trophy and Boo would be missing. They look around and the trophy would start to float. Boo then appears under it to Luigi's relief as Mario laughs in amusement. The Mario Bros. themselves are then surrounded and levitated by multiple other Boos as the main Boo flies up to the screen and holds the trophy. Boo's taunt is to wave its racket while laughing. Boo's offensive power shot is the Boo Blast and its defensive power shot is the Boo Brigade Return.

Mario Tennis Open
Boo reappears in Mario Tennis Open, where he is again a playable and starting participant. He is one of the only two Tricky characters alongside Bowser Jr..

Mario Tennis: Ultra Smash
Boo appears in Mario Tennis: Ultra Smash as a default playable character. He is once again a Tricky character.

Mario Tennis Aces
Boo returns as a playable character in Mario Tennis Aces. Like in previous Mario Tennis games, Boo is classified as a Tricky character. His Trick Shots are Roundabout and Through It All, while his Special Shot is Illusion. Boo also has unlockable alternate costumes, coming in the form of visors, that can be unlocked by playing the “Boo Hunt” co-op challenge. In this challenge, the player must hit boos at the other side of the court to get coins. The visors came in Blue, Green, and Purple and require 2,500 coins, 10,000 coins and 20,000 coins respectively.

Paper Mario series
Boos have appeared in every game in the Paper Mario series, where they are usually found in ghost houses, like in the other Mario games. In the first three Paper Mario games, the Boos appear with a design similar to Bigger Boo from Super Mario World 2: Yoshi's Island. In the latter three games, they use their modern appearance from Mario Party 4 and onward.

Paper Mario


Boos appear in Paper Mario as friendly but tricky characters. White Boos live in Boo's Mansion, and yellow Boos live at Gusty Gulch. Their princess is Lady Bow, who lives in Boo's Mansion along with Bootler.

At first, Boos were being eaten by Tubba Blubba. Some Boos tried attacking the monster to save their friends, but they failed because of Tubba Blubba's "Invincibility". Seeking help from Mario, they captured Skolar, the Star Spirit Mario was trying to save in order to have Mario help them.

In the game, when Mario arrives at Boo's Mansion, Bootler tells him to get to the third floor. Boos have prepared some puzzles for him under the order of Lady Bow to test him. One puzzle is for Boos to form a rotary circle, throw an item several times and ask Mario to guess who is holding the item. The first time he opens a door a big Boo appears on the screen. In the eastern room of the second floor Boos holding a Record play this trick. In the western room of the second floor, a Boo is guarding a chest box with a Weight in it. Mario plays the Record to lure the Boo away and uses the Weight on the droplight of the mansion to open the western door on the first floor. Boos in the basement hide in a big chest box in the basement. When Mario opens the chest box, they play the puzzle with Super Boots. After Mario gets them, he is able to get Boo's Portrait with which he is able to get to the third floor. There, Lady Bow asks Mario to help the Boos to defeat Tubba Blubba as a condition to free Skolar, and joins Mario's party to assist him.

In addition, a Boo appears after Mario got the Super Boots and tells him how to get the Star Pieces underground. And some Boos are flying in the sky who can be seen out of the windows. When Mario is about to set off, two white Boos appear to open the gate to Gusty Gulch under the command of Bow.

In Gusty Gulch, upon Tubba Blubba's arrival, the Boos hide but Stanley is late and is caught by Tubba Blubba, eaten.

In the basement of Tubba Blubba's Castle, a yellow Boo tells Mario not to fight Tubba Blubba until he finds his weak point. According to his word, he sneaked into the castle to look for the weak point. After Mario gets Yakkey, 3x2 peasant Boos appear in front of Tubba Blubba's Castle and, seeing Mario and Bow get out and Tubba Blubba chasing, help the co by blocking the door.

After Tubba Blubba is defeated, the Boos he has eaten are saved, and Bootler releases Skolar as promised. Boos rejoice, and the background music in Boo's Mansion is replaced with a cheerful one. The Boos at Gusty Gulch write Lady Bow an admiration letter, which the player can read at the Toad Town Post Office. They also begin to talk about a female Boo called Victoria.

After Mario defeats Bowser, two Boos come to Peach's Castle to see the party, one white and one yellow. The white one says he comes to see Lady Bow in her finery. He thinks that Bow is prettier than Princess Peach. The yellow one says he's going to have a wedding ceremony after the party. In the end-of-game parade, three white Boos along with Bootler are carrying Tubba Blubba's body.

Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Boos are enemies for the first time in the series. They are found in Creepy Steeple and levels 21-29 of the Pit of 100 Trials. When Mario first enters the steeple there is only one Boo in the room who says that he misses his friends. He will let Mario through only one door (blocking him from using any other doors), where he finds a chest. When he opens it, 200 Boos fly out. The last Boo asks Mario "How many Boos came out of that chest?" If Mario answers correctly the Boo will give him an Ultra Shroom. If Mario is wrong the Boo will give him one coin. Upon returning to the main room, the first Boo is still there. He asks if Mario is going to be mean to him. If Mario answers "No", a bunch of Boos (the same ones from the treasure chest) will start flying around the main room, attempting to swarm Mario. If successful, they will throw Mario out of the Steeple, exactly like the Sentinels in Tubba Blubba's Castle. If Mario Spin Attacks them several times, they merge into an Atomic Boo. Once the Atomic Boo is defeated (releasing a Lucky Start badge), Mario can fight Boos in other parts of the Steeple. Even before defeating the Atomic Boo, Boos can still be found, but only when accompanying Swoopers.

The original Creepy Steeple Boo sends an e-mail to Mario that thanks him for freeing his friends, despite the fact that they attacked him. He signs the letter "The Creepy Steeple Boo". More Boos can be found in the Pit of 100 Trials. In this game, Boos attack by becoming invisible and getting close to Mario or the partner, then becoming visible and making a glare at them, causing 3 damage. However, if Mario or his allies gets lucky in battle, the Boo who tried to attack Mario and his partner will be tired out. The game also introduces a more powerful sub-species, the Dark Boo, which can be found in Poshley Sanctum.

Field Tattle
Outside of battle, Goombella can use Tattle only on a Boo found in the foyer of Creepy Steeple after Mario releases the 200 Boos.
 * "That's a Boo. You think it's one of the Boos from that box?"

Super Paper Mario
Boos return as enemies in Super Paper Mario. In this game, they turn invisible if Mario looks at them, but they turn visible and chase him if he is not looking at them, similar to their behavior in Super Mario 64. To defeat them, the player must approach them from the back and then attack them. Additionally, the Flipside Arcade houses a Boo themed shooting game, Mansion Patrol. This game has the player shooting Boos, including Dark Boos and occasionally Atomic Boos, to score points. A Toad frequently appears to give power-ups, as long as the player saves him from his Boo captor. Lady Bow also makes three cameos in this game.

Paper Mario: Sticker Star
Boos reappear in Paper Mario: Sticker Star. They only appear in World 4-3: The Enigmansion. Mario must use the Book of Sealing, given by a Toad, to seal away every Boo that has escaped. In battle, Boos can make themselves disappear and can slap Mario or they can go up to Mario and scare him by making a scary face. They are able to make Mario dizzy in this game with their scare attack preventing him from using any of his defensive/dodging stickers. The attack is determined by the sound the Boo makes when it disappears.

Among the normal Boos, there is one golden Boo that drops several Coins after Mario defeats it, which can be found in the safe. This Boo attacks exactly like the normal ones. Another notable Boo is one that is crumpled, which is found in a trash can. In battle, it only has 1 HP and cannot attack. Additionally, a group of eighty-two Boos called a Boo Stack also appears. Once all the Boos get returned to the book and it is placed in its rightful spot, Kamek appears and turns all the captured Boos into the mini boss, Big Boo. After defeating the mini-boss, the Boos are put to rest once again and the mansion is restored to its former state. Boos can no longer be fought at this point.

Paper Mario: Color Splash
Boos return in Paper Mario: Color Splash as enemies who can be fought in the parallel universes of Vortex Island, Lighthouse Island and Fortune Island. In battle, they attack by either hitting Mario or scaring him. They can disappear while in battle, causing all attacks to miss until they reappear. Outside of battle, if one is stared at too long, it will disappear, and then reappear behind Mario. A Boo appears as an NPC in Redpepper Crater, where it is in a hot spring. A Boo 10-Stack variant also appears.

Paper Mario: The Origami King
Origami Boos appear as enemies in Paper Mario: The Origami King, first encountered in the Scorching Sandpaper Desert, but only at night; after Mario has explored the Temple of Shrooms and put the sun back in the sky, they are replaced by Bone Goombas. In battle, Boos will turn invisible right before Mario manipulates the arena, forcing him to memorize their positions. However, they will reveal themselves if they are hit by a Toad's thrown object or shortly before time runs out. In addition, much larger Paper Macho Boos appear in the desert at night, replaced by Paper Macho Paratroopas by day. A Paper Macho Boo is also featured as one of the seven opponents on Scuffle Island.

Luigi's Mansion
In Luigi's Mansion, Boos are the main antagonists. This game also introduces the Boo leader, King Boo. King Boo sends a letter to Luigi, stating that he had won a mansion in a contest. However, Luigi does not enter any contest, but pays no attention, and heads off. Mario goes on ahead but gets captured by the King of the Boos, King Boo. Luigi has to rescue him from the Boos, using E. Gadd's Poltergust 3000. Luigi manages to find his brother, stuck in a painting. He ends up having to battle King Boo in order to rescue Mario. King Boo sends them to the roof of the mansion and uses a Bowser suit to battle him. However, the suit's head can come off once a spikeball is thrown at him, and King Boo would float out, leaving him open for Luigi's Poltergust 3000. After taking away all of his 500 HP, King Boo is turned into a painting, and Mario is restored back to his normal self. However, King Boo manages to escape by unknown means and reappears in several future Mario games.

There are 50 Boos (51 including King Boo) which Luigi must suck up in the Poltergust 3000. Of these, 15 of them are smaller ones that make up the portrait ghost Boolossus, with King Boo as the final Boo. Unlike the other ghosts in the game, Boos will appear in a room, even when the lights are on. When Luigi attacks them, they usually run away, but occasionally twirl into him to cause damage. All of the 36 Boos, excluding King Boo and counting Boolossus as one Boo, have puns in their names.

The Boos in Luigi's Mansion seem to be the reverse of the Boos in the Super Mario series: while the Boos in the Super Mario series sneak up on Luigi when he is not looking and then disappear/hide when he looks at them, the Boos in Luigi's Mansion (excluding King Boo and Boolossus) hide when Luigi's not looking at them and then they face Luigi when he finds them. One of the Boos, PeekaBoo, references the fact that Boos are notorious for hiding.

Luigi's Mansion: Dark Moon
Boos appear in Luigi's Mansion: Dark Moon. They have names that play on "Boo" as in the first game. King Boo appears, having a similar appearance to that of his debut. They have the ability to create Spirit Balls which can make objects invisible until exposed with the Dark-Light Device. All of the regular missions in the game have a Boo in an object that is invisible, and Luigi must find it by revealing the invisible object with the Dark-Light function of the Poltergust 5000; the Boo appears after the revealed Spirit Balls have been vacuumed up. However, not all Boos are hidden in invisible objects.

To capture a Boo, Luigi must expose it with the Dark-Light, vacuum and pull on the Boo's tongue, and release it with the Button, damaging the Boo as it bounces around the room. When it reaches 0 HP, the Boo can be sucked up; it sticks onto the nozzle, and Luigi presses the Poltergust 5000 against the ground to shove it inside. When Luigi returns to the Bunker after completing a mission, any captured Boos are sent to the Boo Canister in the Vault. After all Boos in a mansion have been captured, a bonus mission is unlocked for the corresponding mansion. There are a total of 32 Boos, 33 if counting King Boo, 10 of which merge into the Big Boo fought in the Treacherous Mansion.

Luigi's Mansion 3
Boos return in Luigi's Mansion 3. Like in previous entries, they have "Boo"-inspired names, and King Boo returns as the main antagonist.

There is one Boo found on each floor (except for the Master Suite), which appears after Luigi has obtained that floor's elevator button. The exact location of each Boo is randomized. To help find a Boo, Gooigi will begin to vibrate, corresponding with the player's controller, when next to the room with the Boo in it. There is also an item in the game known as a Boo Finder, which reveals the location of a single Boo. Once Luigi enters the room with the Boo, the music will change and he must uncover the object with the strongest vibrations, which causes the Boo to appear and seal all exits until caught. If a wrong object is uncovered, the Boo will launch a swarm of bats at Luigi and flee to a different room. Once revealed, Boos attack by either spinning towards Luigi to deduct 20 HP or by throwing a bomb at him. To capture the Boo, Luigi must expose it with the Dark-Light device, then pull on its tongue and slam it repeatedly. All Boos have 20 HP.

Mario & Luigi: Superstar Saga / Mario & Luigi: Superstar Saga + Bowser's Minions
In Mario & Luigi: Superstar Saga, Boos are enemies that only appear in Bowser's Castle; they aid Bowletta along with the rest of the minions who believe her to be Bowser. Outside of battle, they hover around, attacking Mario and Luigi when they are not looking. However, they look away if Mario or Luigi make eye contact. The Boos also show the ability to teleport. In battle, a Boo has two attacks. For the first attack, the Boo will teleport in front of one of the brothers and attempt to bite him. For the second attack, it will fly up into the air and swoop into one of the Mario Bros., which can even prohibit the use of certain moves or items. The former attack can be countered with Mario or Luigi's hammer, whereas the latter can be dodged or countered by jumping. In either of these attacks, if the Boo makes a face, it will target Luigi, if it does not, it will target Mario. Boos are weak to Firebrand and Fire Bros. They also have low HP, but very high defense.

Boos wearing mining helmets and brandishing pickaxes also appear in levels 4 and 5 of Mysterious Mine Carts. If these Boos touch Mario, they will cause the loss of a diamond. They will slowly shrink until they disappear if the flashlight is pointed at them.

Boos appear in the main game and in Minion Quest: The Search for Bowser from Mario & Luigi: Superstar Saga + Bowser's Minions. Boos are flying troopers, and attack by ramming into enemies. Their Special Skill, Evasion Cloak, allows them to increase their evasion, depending on how filled the meter that is shown becomes. Captain Boo appears as a playable captain in the game. When a Boo appears as a captain, they are able to attack the other captain from behind, using Sneak Attack.

Mario & Luigi: Partners in Time
During the events of Mario & Luigi: Partners in Time, Boos appear in Bowser's Castle of the past. Mario, Luigi, Baby Mario, and Baby Luigi meet a lot of them while trying to reach the end of Baby Bowser's Castle. In the field, Boos attack the same way as they did in Mario & Luigi: Superstar Saga, but in battle, they fight differently, and have significantly decreased defense. They cover their faces, but when they start to attack, the Boo would take one of its hands off one of its eyes, showing who it is about to attack. If it shows its right eye, it will attack Mario, but if it shows its left eye, it is attacking Luigi. Then it would appear from behind and charge towards one of the Mario Bros. However, this could easily be countered with a jump. If the attack was not countered then the boo will steal an item that can only be recovered by defeating the boo. After a turn for each brother, the boo would Flee with the item. They also appear during the battle with Sunnycide. After the Mario Bros. flip the egg monster over, Sunnycide could summon a Boo to attack Mario or Luigi. Dark Boos also return in the game, and are found in the Gritzy Caves. Also, when a Handfake has a Bowser sign, a Boo or a Fly Guy carries a flame from Bowser's mouth.

Mario & Luigi: Bowser's Inside Story / Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey


Boos make a reappearance in Mario & Luigi: Bowser's Inside Story. They appear in Bowser's Castle, where they have been brainwashed by Fawful along with the rest of Bowser's minions once he took over the castle. When Bowser gets to have a feast as a reward for beating Midbus at the Fawful Theater show, three Boos serve him food cooked by Fawful himself. However, Bowser is tricked into eating too much food and ends up getting fat, which results in him getting stuck in the floor due to his weight. Boos reappear later in the game to help many of the brainwashed minions of Bowser push the Fawful statue against him. In addition, a Boo appears whenever Bowser gets a level up. The Boo (just like the Fishin' Lakitu in Mario's or Luigi's level up screen) holds the circle for getting a bonus upgrade for the stat of the player's choice.

An odd thing shown in the game is a Boo and Koopa Troopa in love with each other in Bowser's Castle. They not only love each other, but also love Fawful due to the brainwashing that was put on the minions.

Yikk, a ghost who appears in the same game at the Tower of Yikk, explains that he researches Boos. He even builds a machine to visualize Boo transparency waves before he passed away.

During the fight with Bowser Memory ML, Bowser Memory L has an attack that involves a square shaped, pixelated version of a Boo chasing him around. The Boo can be jumped on by either Mario or Luigi to stop the attack prematurely.

Boos return in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, where they additionally are found as enemies and recruitable allies in the Bowser Jr.'s Journey mode. Their special attack is Discord, which lowers the speed of enemies.

Mario & Luigi: Dream Team
While Boos themselves do not appear in Mario & Luigi: Dream Team, an item named Boo Biscuit does.

Mario & Luigi: Paper Jam
Boos appear in Mario & Luigi: Paper Jam in a minigame where the player has to save a Toad by running away from a Boo and avoiding firebars and bombs. Like in many other games, this Boo will stop if the Mario Bros. look at it, and will follow them if they look away. Boos can also be seen carrying Papercraft Boos, along with Papercraft King Boo. Their paper versions also appear as regular enemies in the haunted side of Gloomy Woods. King Boo also appears as a boss in Gloomy Woods. Boo Biscuits also return from Mario & Luigi: Dream Team.

Mario vs. Donkey Kong
A Boo appears in Mario vs. Donkey Kong, acting similar to their other appearances in platforming games. They only appear in both segments of Level 4-4 and in Level 4-4+. They cannot be defeated, and if they manage to defeat Mario or the Min-Mario, the Boo will grow and stick its tongue out.

Mario Pinball Land
In Mario Pinball Land, Boos appear in certain areas in the game. Mario cannot hit them at the front because they will become transparent as Mario passes through them. If Mario hits one of the Boos on its back, the Boo disappears and it is worth 2,000 points. They occasionally will disappear and reappear to another spot in the area.

A Big Boo also appears as one of the game's bosses. He is the boss of the haunted house and can only be damaged by hitting it from behind.

Yakuman DS
Boos appear in the Japan-only Nintendo DS game, Yakuman DS. They are one of the many opponents. Other opponents include, Goomba, Diddy Kong, and Hammer Bro. Boos are not unlockable or playable. They are opponents from the start of the game.

Dance Dance Revolution: Mario Mix
Some Boos make appearances in Dance Dance Revolution: Mario Mix in both regular and giant varieties. Their objective is to try to make Mario miss a step. If successful, they block Mario's next move. Mario is able to step on regular Boos to hold them back, but he cannot do the same to their gigantic counterparts.

Mario Baseball series
Boo makes its first baseball appearance in Mario Superstar Baseball. It is on Wario's team as a starter. Boo is tied with Peach with its pitching, losing only to Bowser and Waluigi. Its special running and fielding move is a Super Jump. Its running and batting are weak, but its fielding is very poor. The only worse fielder in the game is Bowser.

Boo makes another appearance in Mario Super Sluggers. It is on Wario's team once again, and it can be unlocked in Wario City by finding it in between boxes and completing its challenge. Like its predecessor, Boo has the highest ranked pitch in the game, along with Peach (9/10). Despite its pitching being very high, its stamina is very poor, but its other stats range from average to low. Boo displays good chemistry with King Boo, Shy Guy, Magikoopa, and Blooper. Its chemistry with Luigi, Yoshi, Baby Mario, and Baby Luigi is bad.

Also, a new item, called Mini Boos, appears. When activated, Mini Boos turn the ball invisible for a short period of time. If used against a computer, the player stops moving until the Boos go away. If used when a special hit is in effect, the Boos do nothing.

Super Princess Peach
Boos appear in Princess Peach's first starring game, Super Princess Peach. They act as normal Boos, hiding their face when Peach looks at them and attacking when Peach has her back turned. However, there is an angry variety called the Mad Boo, which attacks the opposite way. They attack when Peach looks at them, and gander around for her when she looks away. Big Boos and their vibe counterparts, a new species called Mad Big Boos, also appear.

King Boo also appears, as one of the bosses of the game. He will attack Peach by shooting fireballs at her, but she can use these to light the candles on the wall, damaging him. His vibe during the game is Gloom, which he will use to douse the candles.

There are several sections of the game where a mass of Blindfold Boos will charge towards Princess Peach.

Mario and the Incredible Rescue
Boos make an appearance in the chapter book Mario and the Incredible Rescue. The cover features two Boos. One of the Boos is from Mario Kart: Super Circuit and the other is a mirrored Boo from Luigi's Mansion. They are known as "ghosts" in the book. Boos capture Princess Peach and take her to Bowser's Castle. Mario also sees a vision of Princess Peach being caged and surrounded by six Boos. Boos are eventually defeated by Mario at the end of the book. To defeat them, Mario casts a spell on them and sends them flying out of the castle.

Tetris DS
Boos also appear in the Nintendo DS game, Tetris DS. They are one of the few multiplayer items. Boos are able to block the opponent's sight of the upcoming block, making it harder for the opposing player to see the upcoming block. They do not appear in single player mode.

Mario Hoops 3-on-3
Boo makes an appearance in Mario Hoops 3-on-3. It appears as an unlockable character. It is unlocked by beating the Flower Tourney on hard. Boo's special ability is the Thriller Dunk. This is performed by tapping a B-like shape twice. In the game, Boo is classified as a tricky character. The other tricky characters are Paratroopa, Fly Guy, Black Mage, and Moogle. Boo is also one of many of the unlockable characters to not have a baller name.

Mario Strikers Charged
Although Boos do not appear in Super Mario Strikers, they do appear in its sequel, Mario Strikers Charged. Boos, along with Hammer Bros., Toads, Koopa Troopas, Birdos, Dry Bones, Monty Moles, and Shy Guys, are sidekicks to the many captains. They appear with a helmet with the logo of their team captain. Boos are classified as a playmaker. The only other playmaker sidekicks are Toads. Their skillshot is Possess. The given description of the Boos is: "This ghost can fly up and down the sidelines with great speed, using precise and accurate passing to lead his team to victory. His long-distance shots are quite weak though and his hits are not very powerful. If Boo gets a chance, he can Possess the ball and score at will." Boo's appearance in this game resembles that of the Spooky Speedster.

Mario & Sonic at the Olympic Games
Boos appear alongside various other species as members of the crowd in both versions of Mario & Sonic at the Olympic Games. A Boo will also appear to penalize the player if they perform two consecutive fouls in the 100m event in the Nintendo DS version, as well as blocking one of the baskets in the Dream Basketball event when a Chaos Emerald is used. Boos appear as one of the characters to be sorted in Conveyor Belt, as well as one of the enemies to be hit in Shoot!, where they can become temporarily invulnerable.

In the Wii version, Boos appear as an item in Dream Race, where they will follow the character in first place, or second if the player is leading when they use the Boo, for a short amount of time and cause them to lose speed and remain at a low speed. Multiple Boos can follow a character at once, causing them to remain at a lower speed, and can be removed early by using a High Speed item.

Mario & Sonic at the Olympic Winter Games
In the Nintendo DS version of Mario & Sonic at the Olympic Winter Games, Boos appear as items in Ski Cross Racing, where they can be used to steal Rings and items from characters in front of the player. In Extreme Snowboarding, Boos steal items from opponents in front of the player, as well as depleting the energy in their trick gauge. In Ski Shooting, Boos will simply steal an item from an opponent if they have any when the item is used. King Boo also appears as a rival in both versions of the game.

Mario & Sonic at the London 2012 Olympic Games
Boos appear in the London Party mode of the Wii version of Mario & Sonic at the London 2012 Olympic Games, where they can be spoken to in order to play minigames and earn stickers, and also appear in some of the minigames as well. A jersey featuring a Boo design can be unlocked for Miis to wear.

In the Nintendo 3DS version, a Boo first appears in the Story Mode trying to scare people away from the Tower of London with the Phantasmal Fog, and is then followed by Sonic and Tails who challenge the Boo and King Boo to an Olympic Event, with the Boos fleeing when they lose. A single Boo also appears at the opening ceremony. A Boo also appears in Mario's Defeat?!, in which it fails to bring Mario to the London Tennis Club but helps set up the match with a Goomba transformed to look like Mario, and later celebrates with the other minions when they notice that Bowser seems to be back to his usual self. A badge of a Boo can be obtained from the badge machine, and they're also referenced on Luigi and King Boo's badge descriptions.

Mario & Sonic at the Rio 2016 Olympic Games
Boos appear in Archery Plus in the Nintendo 3DS version of Mario & Sonic at the Rio 2016 Olympic Games, where they carry around the targets and disappear once they have been shot.

Super Smash Bros. Melee
In Super Smash Bros. Melee, Boo appears as a collectible trophy.

Super Smash Bros. Brawl
As well as appearing as a trophy in Super Smash Bros. Brawl, Boos make cameos in the Luigi's Mansion stage. When a part of the mansion is knocked down, Boos are seen flying out. Boo from Mario Tennis also appears as a collectible sticker.

Super Smash Bros. for Nintendo 3DS / Wii U
Boo appears in the form of a collectible trophy in Super Smash Bros. for Nintendo 3DS and Super Smash Bros. for Wii U. In the latter, Boos return in the Luigi's Mansion stage from Super Smash Bros. Brawl, and they appear as Smash Tour items: when used, the player starts a battle invincible.

Super Smash Bros. Ultimate
Boos are seen again in the returning Luigi's Mansion stage. A Boo appears in Super Smash Bros. Ultimate as a Novice-class Neutral-type primary spirit, using the artwork from New Super Mario Bros. U. In World of Light, it is found in the Dracula's Castle sub-world of the Dark Realm. The spirit battle takes place on the Mushroom Kingdom U stage, with an invisible grayscale Kirby as the puppet fighter. The spirit can be enhanced to a King Boo spirit at level 99.

Mario Sports Mix
Boos appear in Mario Sports Mix. They appear as the only members of the crowd in Luigi's Mansion circling around the court. Their appearances are in Basketball and Volleyball matches and their laughs can also be heard during the game. Mainly, they can be heard when the player gets a point.

Captain Toad: Treasure Tracker
Boos return in Captain Toad: Treasure Tracker and its Nintendo Switch and Nintendo 3DS ports, functioning the same as they did in Super Mario 3D World with a few minor tweaks. Despite still chasing the player when not watched, Boos and Big Boos can easily be destroyed with Toad's or Toadette's headlamp. Additionally, using a Double Cherry to shine two headlamps on a Boo will defeat it much faster, within a quarter of a second.

Interacting with Boos on the touch screen or with the pointer functionality will cause them to disappear until the player points away. Unlike most enemies in the game, holding the pointer on Boos for however long will not reward a coin.

Mario Sports Superstars
Boo appears as one of the starter captain-type characters in Mario Sports Superstars. In most sports, he is classified as a Technique type character, sharing this attribute with Peach, Daisy, and Waluigi. As such, he excels in aspects such as shot accuracy or horse control. In tennis, Boo is instead a Tricky type character, as per his appearances in the Mario Tennis series, alongside Bowser Jr. and Rosalina. His rallies have a tendency to curve, making it tricky for the opponent to predict the trajectory of his shots. In golf, Boo's default drive is 213 yards, and his shots travel medium-low in a draw trajectory.

Mario + Rabbids Kingdom Battle
Boos appear as obstacles in certain areas in Mario + Rabbids Kingdom Battle. They warp to certain areas during the turn transition between the heroes and enemies. If a Boo converges on a character, it will follow said character and force them to warp to a random spot on the battlefield along with the Boo. Additionally, one of Rabbid Mario's Melee weapons has a design based on a Boo, and in Spooky Trails, several Boos can be found ensnared by ghostly chains, as well as a Boo Balloon that was merged with a Rabbid and a phonograph, becoming the Phantom.

Dr. Mario World
The Boo assistant was added on October 31, 2019. Its effect in stage mode is to fill the skill meter faster when yellow viruses are eliminated, where it fills more at higher levels. The percentage determines the number of points the skill meter fills, so for example at level 3, it fills 30% faster, meaning that for each yellow virus eliminated, an extra 0.3 points is added to the skill meter. In versus mode, its effect is to increase the speed the skill meter fills for both the user and their opponent, in which the amount of points required to fill the skill meter is reduced by the listed percentage. If both players use this assistant, the effect stacks. The resulting amount of points required to fill the skill meter is rounded down to the nearest round number.

A Boo was added as a doctor under the name Dr. Boo in Dr. Mario World on September 24, 2020. His skill is represented by the Boo shielding his face, after which he shows his face and tongue. In stage mode, he immediately eliminates objects in a random 2 x 2 area, similar to Dr. Fire Rosalina's skill but it affects a smaller area. In versus mode, he eliminates objects in a 1 x 1 area at level 1, a 2 x 2 area at level 2 and a 3 x 3 area at level 3 to 5 (the skill meter fills faster at higher levels). This skill prioritizes areas that contain viruses, but if there are no more viruses, the area in which is targeted will be random as long as it contains at least one object.

Minecraft
In the Super Mario Mash-up in Minecraft, Ghasts are replaced by Boos.

Monopoly Gamer
Boo is a playable character in Monopoly Gamer. He is sold separately as a "Power Pack" expansion figure.

The Legend of Zelda: Link's Awakening


Boos make a cameo in The Legend of Zelda: Link's Awakening, only appearing in a dark room in the games' second dungeon, Bottle Grotto. They actively chase Link regardless of whether he is facing them or not; if Links swings his sword at them, they disappear and reappear at a different location. After Link lights up the room, they become vulnerable and can then be defeated with Magic Powder. In the Nintendo Switch remake of the game, they now use their voice clips from the Mario franchise, and a Boo figure can be won from the Trendy Game after clearing the Key Cavern and placed in the Quadruples' house. The text that appears upon acquiring the figure reads, "You got a Boo figure! As spooky ghosts go, this one's pretty cute!"

Appearance
Though their specifics change from game to game, Boos are usually bashful, cowardly, spherical ghosts. They have black beady eyes and fangs. Although they are typically white, there are sub-species of the Boo race that appear in different colors, such as pink. From Luigi's Mansion onward, it became common to picture Boos sticking out their tongues. Boos often have wide open grinning mouths with their tongue sticking out. In most games, Boos are unable to change their facial expressions. The only exception is when they are looked at, in which case they bashfully cover their faces. However, the Luigi's Mansion and early Paper Mario games portray Boos as being more expressive than in other games, being able to frown, scowl, or even smirk. Since Super Mario 64, Boos have been portrayed with a unique, high-pitched laugh. Interestingly, both this laugh and Bowser's laugh are derived from the same stock recording of a human man laughing; it was sped up for the Boos and slowed down for Bowser. Said laugh was coincidentally provided by none other than Charles Martinet, years before his debut as Mario. However, Boos got a new laugh starting in Mario Power Tennis provided by Sanae Suzaki being more of a haunting laugh than before. Although most species of Boo will cover their faces and become intangible when looked at, they will often sneak behind their victim and strike when their back is turned. Due to their ghostly abilities, Boos are generally invulnerable and cannot be harmed by ordinary means of attack. Despite this, they are not invincible and are especially vulnerable to the light. If they are exposed to a source of light, Boos are usually weakened, and in some cases, they may even be defeated. Usually, they can also have other weaknesses. Because of their intolerance to the light, Boos will often hide if they are trapped in lit rooms. However, King Boo claims that Boos cannot truly be killed. While the ghosts generally appear to be more afraid of their victims than their victim is of them, this is not always the case. Some Boos have absolutely no problem meeting their victim's gaze, and will even try to attack. Boos tend to have a taste for the fine arts, as seen in Paper Mario and Mario Party 4. In Luigi's Mansion: Dark Moon it is shown that Boos will actually save someone if only later to trick them. This is seen when Luigi watches through pipe in the Old Clockworks as a Yellow Toad balances on a ledge. Some Boos appear and watch the Toad before it falls off the ledge, which is later found to be quite a drop, the Boos show a large amount of concern and shock when this happens before diving down for the Toad. The Toad is later found in a painting because of the Boos.

Boos are often characterized by their sub-species despite their similarities in appearance and attack manner. Boo species tend to vary wildly in size, with some such as Boo Buddies being miniature, while others such as the Big Boos boast gigantic size.

In Luigi's Mansion, Professor E. Gadd notes that Boos have mysterious powers that increase when they gather together in large groups. While it is difficult to stop them, they can be weakened if one is able to defeat members of the group. Although in Luigi's Mansion: Dark Moon this does not seem to affect them or King Boo in any way suggesting that they do not always need to be in groups anymore.

Boos have few predators, their only known threat being a Spike named Tubba Blubba in Paper Mario, when he began devouring Boos. This, however, may have been his revenge for the countless times the ghosts scared him.

Tools

 * Boo's Sheet - ''Paper Mario: The Thousand-Year Door
 * Fright Bomb - ''Super Mario RPG: Legend of the Seven Stars
 * Boo Bell - ''Mario Party 2
 * Boo's Crystal Ball - ''Mario Party 4
 * Boo Biscuit - ''Mario & Luigi: Dream Team

Habitat
Boos typically make their homes in dark forests, such as the Forever Forest and Boo Woods, and tend to be most commonly found in older buildings such as mansions, castles, and Ghost Houses. Although most of them live in such dwellings, they also seem to enjoy wastelands. One of the only known Boo villages lies in Gusty Gulch. They are typically found in groups because their fears make them find strength in big numbers.

Allegiance
Though most Boos tend to side with Bowser and King Boo, they seem to, for the most part, actually stand as neutral. For example, Boos are by now a common enemy in most side-scrolling games; however, in the Paper Mario series and now increasingly in the multiplayer games, Boos have been seen to take the side of the Mushroom Kingdom. Lady Bow, in fact, helped Mario save the kingdom in Paper Mario. In another example, the Boos in the Creepy Steeple from Paper Mario: The Thousand-Year Door attack Mario initially, but later in the game Mario is sent a friendly letter from one of them. King Boo, on the other hand, has several times been shown to wish nothing but terrible things for Luigi (but this could be accredited to Luigi being easily scared, making him a prime target for most Boo antics). They also have attacked Bowser in some games, such as the Mario Party series, mainly from Mario Party 5 to Mario Party 8.

Language
As hinted in the game Super Mario Galaxy, Boos have their own unique language called Booish. It most probably is spoken only by Boos since Mario cannot understand it. However, upon absorbing a Boo Mushroom and turning into Boo Mario, he gains the ability to read it, if not speak it as well.

Paper Mario also features Boos replacing certain words with "Boo", possibly as a part of the Booish language:

''I am so bored!! Boo-ored!

''Boo-st of luck!

''Hey, what can I Boo for you?

''It's going to be the most Boo-tiful wedding ever!

Mario Superstar Baseball information

 * Type: Technique
 * Starting Team Captain: Wario
 * Status: Player
 * Stats:
 * Batting: 3/10
 * Pitching: 8/10
 * Fielding: 2/10
 * Running: 4/10
 * Player Profile:
 * Strength: Pitching
 * Special Talents: Super Jump
 * Trajectory:
 * Field: Center
 * Height: Normal
 * Star Pitch: Curveball
 * Star Swing: Center
 * Sweet Spot: The Boo face on the bat
 * Compatible Relationships: Wario, Magikoopa, King Boo
 * Bio: "Bowser's underling ghost. Behind the scary face lies a very shy soul. Look most Boos in the eyes and they'll cover their faces...but turn around and they'll attack you! Boos confuse their enemies by flickering in and out of the visible realm, appearing at inconvenient times."

Trivia

 * Creator Shigeru Miyamoto got the idea for Boo from the wife of his coworker and close friend Takashi Tezuka, as she is shy but one day got very angry with him for coming home late from work.
 * Mumbies and Scarfies, enemies from the Kirby series, each attack in an almost identical way to Boos.