From the Super Mario Wiki
A Poison Mushroom (alternatively Poison Shroom), also known as Cursed Mushroom in Mario Party 5, Mario Party 6 and Mario Party 7, is a harmful variety of Mushroom. Usually, they have the opposite effects a Super Mushroom may have, and while they are sometimes called a power-up, they act more like a hindrance or trap. They first appeared in the Japan-only game, Super Mario Bros.: The Lost Levels, which first came to North America on the SNES in the game Super Mario All-Stars, and have appeared in a number of games since then.
Super Mario series
Super Mario Bros.: The Lost Levels
Poison Mushrooms made their debut in Super Mario Bros.: The Lost Levels. They will defeat Small Mario or Luigi, revert Super or Fire Mario into Small Mario, and will have no effect on Invincible Mario or a just-damaged invulnerable Mario. Unlike enemies, they disappear when touched and do not award points when Invincible Mario collides with one. As with all Mushrooms, the game will only allow one to be on screen at a time, so a player can get rid of a Poison Mushroom by revealing a Super Mushroom or a 1-Up Mushroom, causing the first one to disappear. Poison Mushrooms can be found in Brick Blocks, ? Blocks, and Hidden Blocks alike, and generally appear as a dull brown, blue, or gray mushroom in the original FDS game (depending on whether the level is set on ground, underground, or in a castle). The original artwork (seen on the right), though, depicts them with a much more sinister appearance, sporting shadowy eyes and a menacing grin. In the Super Mario All-Stars remake, Poison Mushrooms are also known as Poisonous Mushrooms or Blue Mushrooms and appear as blue-skulled, purple-capped mushrooms with angry eyes, making them much more visually obvious. This change to maintain obviousness was carried over to the Super Mario Bros. Deluxe port, though with a red stalk, green cap, and pink skull, and without eyes.
Super Mario Advance 4: Super Mario Bros. 3
Poison Mushrooms reappear in Super Mario Advance 4: Super Mario Bros. 3 as blue mushrooms with white skulls on their caps, and retain their effects from Super Mario Bros.: The Lost Levels, though any higher-tiered forms (Fire, Raccoon, etc.) revert to Super form instead (unless the Red Switch is used). They only appear in the World-e level Vegetable Volley, hiding under grass rather than in blocks.
Super Mario 3D Land
Poison Mushrooms return in the Special Worlds of Super Mario 3D Land, retaining their effects from Super Mario Advance 4. In this game, they somewhat behave like enemies, as they follow Mario or Luigi around until he is in an area that they cannot get to, or they fall into a bottomless pit. They can also be destroyed by fireballs or boomerangs, or by transforming into a statue to make them vanish on contact. Their appearance is that of a magenta-spotted purple mushroom with angry eyes that emits a purple dust (possibly spores) when released and grabbed.
Super Mario Maker 2
Although actual Poison Mushrooms do not reappear in Super Mario Maker 2, a derivative known as Rotten Mushrooms appear in the Super Mario Bros., Super Mario Bros. 3, Super Mario World and New Super Mario Bros. U styles at night in the Ground theme, replacing 1-Up Mushrooms. They act like Poison Mushrooms do in Super Mario 3D Land, though they can also hop up small ledges, and flee from invincible players.
Mario Kart series
Super Mario Kart
Poison Mushrooms (with red-spotted yellow caps, similar to Super Mushrooms in Super Mario Bros.) were also featured in Super Mario Kart as items, however they were only used by the CPU-controlled drivers Toad and the Princess, and not usable by the player. If a player drove into a Poison Mushroom, they would become small, ending up moving slow and vulnerable to other karts in the area, as they could end up squashed if run over by a full-sized kart. An interesting feature of the Poison Mushroom in Super Mario Kart is the fact the player can also return to normal size if they run into another Poison Mushroom; this also works if the player were made small from Lightning by the other player (as CPU players cannot use Lightning in this game).
Mario Kart Arcade series
In both Mario Kart Arcade GP and its sequel Mario Kart Arcade GP 2, the Poison Mushroom returns as one of Toad's special character items. Like in Super Mario Kart, Toad can throw the Poison Mushrooms either in front of him as well as behind him (providing him with advantages in both ways), which causes his opponents to shrink if they come in contact with them. However, unlike in Super Mario Kart, the player can now use them as well. In this game, however, the Poison Mushroom has a black cap with magenta spots, similar to its Luigi's Mansion design.
Poison Mushrooms were featured in the Game Boy version of Donkey Kong, introduced in Stage 4-8. Sometimes, Donkey Kong or Donkey Kong Jr. will throw them at Mario, and sometimes they are contained inside barrels. Whenever Mario comes in contact with one of them, it will cause him to briefly shrink in size, disabling some of his abilities in the process (the ability to swim, climb ladders, etc.). After a few seconds, Mario grows back to his regular size.
Super Mario RPG: Legend of the Seven Stars
Poison Mushrooms reappear in Super Mario RPG: Legend of the Seven Stars as Bad Mushrooms. They can be purchased in Seaside Town while Yaridovich is in control of the town, and can only be used in battle. They can also be obtained after using a Yoshi Cookie on an Amanita or Chewy, and occasionally from Kriffids after defeating them. When used, Bad Mushrooms poison an enemy of choice, though some enemies are immune. Their official artwork depicts them with their above ground Super Mario Bros.: The Lost Levels coloration, while the sprite itself depicts it as a Super Mushroom's modern colors.
Mario Party series
Mario Party 2
In Mario Party 2, during the mini-game Rakin' 'em In, if the player grips and drags a Poison Mushroom into their goal, they lose three points. They are referred to as Poison Purple Mushrooms in the minigame.
Mario Party 3
In Mario Party 3, the Poison Mushroom is an item that the players can use on either themselves or one of their opponents. A player who is cursed by a Poison Mushroom can only roll a 1, 2, or 3 on their next turn. It is possible to eliminate the curse by using another Mushroom or a Magic Lamp. If the player's character is still under effect of the mushroom, Tumble will say that they are still sick from it. It is Waluigi's favorite item. In this game, the Poison Mushroom has an indigo cap with pale lime-green spots.
Mario Party 5
In Mario Party 5, the Poison Mushroom could be found as a capsule. If a character lands on a space where it has been placed or if the player uses it on themselves, they can only roll the die with numbers from 1 to 5. The Poison Mushroom is known as a "Cursed Mushroom" in this game.
Mario Party 6
The Poison Mushroom returns in Mario Party 6, with a small change. It reduces the Dice Block numbers from 1-6 to 1-3 and is exclusive to Solo Mode.
Mario Party 7
Mario Party: Island Tour
Poison Mushrooms were given a minor role in Mario Party: Island Tour, where images of them are stuck on some panels in the puzzle minigame, Emergency Hexit. If not removed quickly, they would consume 5 seconds from the game's timer every once in a while. The player can get rid of Poison Mushroom panels by clearing a row of identical panels that is adjacent to them.
Mario Party 10
Poison Mushrooms return in Mario Party 10, appearing only in the minigame Movin' Mushrooms. If they fall into one of the carts, the respective team loses three points. They retain their Super Mario 3D Land appearance in this game.
Mario Party: Star Rush / Mario Party: The Top 100 / Super Mario Party
Poison Mushrooms are obtainable items in Mario Party: Star Rush, Mario Party: The Top 100, and Super Mario Party, that can be used on other players to subtract two from their dice roll. The effects of this item are capable of stacking.
In Luigi's Mansion, Poison Mushrooms are dropped by Portrait Ghosts when Luigi tries to suck them up. Poison Mushrooms can also be found by vacuuming or interacting with various objects throughout the mansion, and they have a chance of appearing during the final boss battle whenever King Boo's Bowser suit destroys a pillar. These mushrooms bounce around the room for a few seconds before disappearing. On contact, they cause Luigi to shrink and drop ten coins on the floor. Additionally, Luigi cannot use his Poltergust 3000 in this form, potentially allowing the Portrait Ghosts to escape his vacuum and thereby reduce the portrait rank. While in this small state, Luigi's voice clips are high-pitched. After several seconds, the Poison Mushroom's effect wears off and Luigi's size returns to normal.
In the Nintendo 3DS remake, Poison Mushrooms can be turned into Super Mushrooms if Mario's amiibo is scanned.
Super Smash Bros. series
Poison Mushrooms appear as items in the Super Smash Bros. series, starting with Super Smash Bros. Melee. They have a similar appearance to Super Mushrooms, though Poison Mushrooms are duller in color, and feature angry eyes, similar to their debut appearance. They are grabbed upon running into them, and they make the player smaller and easier to KO. While tiny, the fighter's attacks have much less reach, and they move noticeably slower, while being able to jump higher. Aesthetically, the fighter's voice becomes higher-pitched.
Poison Mushrooms also weaken the fighter's attack power, which is more noticeable in Super Smash Bros. Brawl, Super Smash Bros. for Nintendo 3DS / Wii U, and Super Smash Bros. Ultimate, where all direct attacks deal around 0.6x their normal damage.
Mario & Luigi series
Mario & Luigi: Superstar Saga / Mario & Luigi: Superstar Saga + Bowser's Minions
In Mario & Luigi: Superstar Saga, one of the things Trunkle can inhale is a Poison Mushroom. They are colored green with red spots, and poisons a brother if touched. Popple also sometimes throws them from his bag; these Poison Mushrooms cause more severe damage when touched. When the brothers travel to Little Fungitown, Mario eats an Invincishroom, claimed to be a mix of a Starman and a 1-Up Mushroom. However, Mario, being an outsider, is not immune to the dubious concoction and falls gravely ill.
In the 3DS remake, Mario & Luigi: Superstar Saga + Bowser's Minions, the "Invincishroom" (now referred to as an Invincibility Mushroom) that Mario ate and got sick from was revealed to really be a misidentified Poison Mushroom that Captain Goomba and his squad found. Poison Mushrooms themselves retain their Super Mario 3D Land appearance in the remake.
Mario & Luigi: Partners in Time
In Mario & Luigi: Partners in Time, a Poison Shroom can be an item used by the two Dr. Shroobs and also Swiggler in the battle against him. The Shroobs also resemble poison mushrooms. In addition, one of Shrooboid Brat's attacks involves spitting either Mushrooms or Poison Mushrooms at Mario and Luigi, though they are launched as the opposite of what he is given (if he is given a Mushroom, it is spit out as a Poison Mushroom, and vice versa). Like in the previous game, getting hit by a Poison Mushroom inflicts the brothers with the Poison status effect.
Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
Poison Mushrooms also appear in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey where they replace Cheep Cheeps in one of Junker's attacks.
Paper Mario series
Paper Mario: The Thousand-Year Door
Poison Mushrooms, appearing as dull green mushrooms with pink spots, appear in the Paper Mario series, where they are called Poison Shrooms, starting with Paper Mario: The Thousand-Year Door. They're one of the pictures that the player can earn during a Bingo! (and unlike the items, are drawn with faces). If three in a row appear, Mario's HP (as well as his partner's HP), FP and SP will all be cut in half and all of the audience members will leave.
Poison Shrooms as items appear much later in the game. They could be created by Zess T. by mixing a Slow Shroom and Inky Sauce, Point Swap or Trial Stew and a Dried Bouquet. If Mario or his partner eats this mushroom, the user will lose half his HP and be afflicted with the Poison status. In battle, there is a small chance that when eaten, the Poison Shroom won't poison its user, but will restore all HP instead. There is a common misconception that the Feeling Fine badge(s) are required for this to happen, but it is simply a random occurrence.
Super Paper Mario
In Super Paper Mario, Poison Shrooms are a much more common occurrence than in its predecessor, occasionally being dropped by Zombie Shrooms, Cursyas, and their relatives. However, they do not damage the player for half of their HP; instead they gradually do damage 1 HP at a time until the poison is cured. They are used slightly more in recipes; for example, a single Poison Shroom can produce a Dangerous Delight. In addition, any recipe that requires a Poison Shroom can be cooked using a Ghost Shroom instead, if Poison Shrooms are in short supply (Ghost Shrooms can be bought from various shops, or obtained via Merlee's charms).
Paper Mario: Sticker Star
In Paper Mario: Sticker Star, the Poison Mushroom returns as a sticker, having the same appearance as in Super Mario 3D Land. It poisons Mario upon usage; however, the effect will also transmit to enemies that attack him in close combat while it is active. Another one of its effects is that it prevents Mario from wearing defense or evasion stickers such as the Tail, the Shiny Tail, the Super Boot, the Shiny Super Boot, the Frog Suit, and the Shiny Frog Suit.
It is also used as a 'key' to open the door in Drybake Desert to enter the desert. Putting one inside of a Paperization Block will yield three Shiny Leaf stickers. A Toad in a back alley of Decalburg will sell the player a heavily overpriced Poison Mushroom (only once Hither Thither Hill is unlocked), but the player can negotiate to get the price down to 25 coins.
Mario Hoops 3-on-3
In Mario Hoops 3-on-3, Poison Mushrooms appear in Power-up panels. They make the player weak and slower.
Poison Mushrooms are the only obstacles in the DSiWare game Mario Clock. However, they will only appear while the player character is in Super form, so they cannot cause Mario or Luigi to lose a life.
Puzzle & Dragons: Super Mario Bros. Edition
Poison Mushrooms make an appearance in Puzzle & Dragons: Super Mario Bros. Edition, as Dark Orbs, one of the five elemental orbs used in the game's puzzle board. Their design in this game is a hybrid of their appearances in Super Mario 3D Land and the Super Mario All-Stars remake of Super Mario Bros.: The Lost Levels.
They're also used as transformation items for Magikoopas, pairing them with a Dark-element Magikoopa, and for transforming enemies into their skeletal versions.
Profiles and statistics
Super Smash Bros. series
Super Smash Bros. Melee trophy
*Note: This is incorrect. Poison Mushrooms first appeared in Super Mario Bros.: The Lost Levels, but as this was only released in Japan (as "Super Mario Bros. 2"), its inclusion in the compilation game Super Mario All-Stars was the first time it appeared in any other region. In addition, they only cost characters a life if they were small; this implies that they do no matter what the circumstances are.
Super Smash Bros. Brawl trophy
Super Smash Bros. for Nintendo 3DS / Wii U trophy
Blue indicates exclusive to the Wii U version.
Mario Party series
Mario Party: The Top 100
Lowers a rival's roll by 2. Practice saying, "You wouldn't do that to me..." now.
Luigi's Mansion (Nintendo 3DS)
Names in other languages