Mario & Luigi: Bowser's Inside Story

Mario & Luigi: Bowser's Inside Story (known in Japan as Mario & Luigi RPG 3!!!) is the third title in the Mario & Luigi series, after Mario & Luigi: Superstar Saga for the Game Boy Advance and Mario & Luigi: Partners in Time for the Nintendo DS. It is used, like its previous installment, for the Nintendo DS. Unlike its prequel for the Nintendo DS, this game makes greater use of the DS's touch controls and microphone. This is the second Mario & Luigi installment for the Nintendo DS.

Story
The Prologue, from the instruction booklet: A dreadful disease dubbed "the blorbs" has begun to spread throughout the Mushroom Kingdom, causing the citizens to balloon up and roll around helplessly. With even the Star Sprites at a loss for what to do, Mario and Luigi set out to an adventure to find the cure! And then there's everyone's favorite brute, Bowser, who, as always, tries to abduct Princess Peach, and only to be thwarted once again by Mario. Angry at his defeat, he meets a shady merchant deep in the woods who gives him a "Lucky Shroom", with the promise that it will make him really strong. "Strong enough to beath Mario?! Really?!" Bowser swallows the Mushroom in one gulp... and instantly starts inhaling anything and everything around him! Somehow he arrives at Peach's Castle in the state and ends up inhaling the Mario Bros. because of the Mushroom's power. What'll happen to the Mario Bros. inside Bowser's body? And what about the fate of the Mushroom Kingdom?

After the Mushroom Kingdom's citizens begin to fall victim to the "blorbs," a mysterious disease that affects Toads and makes their bodies swell to enormous proportions, Princess Peach summons a conference to find a solution for the problem. The conference is attended by Mario, Luigi, Dr. Toadley's intern, some Toads, and Starlow, a star sprite. As Peach is explaining the effects to the attendees, Bowser barges into the room, trying to be a part of the meeting too. However, since his interruption is interpreted as an attempted assault, he is attacked and quickly defeated by Mario. Peach and Starlow then use their powers to send him away to Dimble Wood. After recovering from his defeat, Bowser receives an item called a "Lucky Mushroom" from a mysterious man in a gray cloak. Unbeknownst to Bowser, the cloaked person is actually Fawful, who tricked Bowser and also was the cause of the blorb epidemic (by selling "Blorb Mushrooms" to the toads). His present quickly turns out to be a "Vacuum Mushroom", an Item which causes strange effects to take place in Bowser's body and enhances his breath. The enhancement gives Bowser the ability to inhale everything, but also allows Fawful to control his actions. Using this newly gained influence, Fawful then sends Bowser back to Peach's meeting, where he uses the Vacuum Shroom's powers to inhale everyone. While gloating about his victory, he mysteriously falls unconscious, and Fawful sends his minion to take him away.

After being inhaled, Mario reawakens inside Bowser's body, being reduced to microscopic size. While traveling through the Trash Pit and encountering a few hostile immune cells, he eventually stumbles into Starlow, and then Luigi. After being reunited, the trio sets out to find Princess Peach. As they try to escape the place, they find a Nubbin, an object resembling an exposed nerve. They activate it by hammering it, which rouses Bowser and breaks his unconsciousness. He awakes inside the Cavi Cape Cave. He starts out of this strange place and soon discovers that he cannot breathe fire. Angry about the loss of his flame, he continues out of the caves. After making his way out of the caves he meets Fawful, who proclaims he is planning to claim Bowser's Castle as his own and to conquer the whole Mushroom Kingdom. Fawful then flees, and before Bowser can give chase, he is halted by Midbus, a minion of Fawful. Bowser battles him, but due to his body weakening because of the Vacuum Mushroom, he is quickly defeated. Bowser then sets out north, towards his castle. Before he can go there, he has to cross Plack Beach which lies between Cavi Cape Cave and his home. Soon after he begins his journey homeward, he is confronted by a mysterious voice explaining the concept of Chakroads to him, portals allowing him to quickly traverse the Mushroom Kingdom.

At Plack Beach, Bowser meets Broque, a famous block collector, trapped on a small island. Initially reluctant, Bowser agrees to help him when Broque offers him the Vacuum Block, an object that gives its user the capacity to use a powerful suction attack. Bowser pulls on the rope connected to the island, but is having difficulty. The bros then help out by boosting his arm muscle. After successfully completing this task, he yanks the island onto the beach. Now rescued, Broque teaches Bowser the vacuum ability. With that new power, he continues north. At the north side, Bowser comes across the Sea Pipe Statue, a fountain dedicated to a hero of the sea. Because it doesn’t look like Bowser, he begins to destroy it. Unbeknown to Bowser, Fawful has imbued it with the power of self defense, and it attacks him. After Bowser deactivates it, the statue turns back into a water fountain. Drinking from it, Bowser inadvertently opens a path allowing the Mario Brothers to advance further into him. They must find the Stingler, a key-like item that opens the path to the Flame Pipe where Scutlet blocks Bowser's flame. After defeating Scutlet, Bowser is able to breathe fire again. He uses this rediscovered skill to continue northward, and defeat Broggy, Broque’s pet dog. Bowser then heads back to Dimble Wood.

In the forest, Bowser runs into Broque again, this time inside Broque's shop. As Bowser is leaving, Broque asks him to do a favor while he's on his mission: to recover some Blitties for him. Bowser also finds some trapped Goombas, which were caged by Fawful. After freeing his minions, Bowser is able to use his newly discovered move, Goomba Storm. Near the end of Dimble Wood, Bowser meets up with three former troops from his army: Sergeant Guy, Corporal Paraplonk, and Private Goomp. They’re attempting to retake the castle using a Banzai Bill cannon, but they don’t have any ammunition. Bowser then heads to a garden maintained by the Wiggler clan. He finds a giant carrot, thinking it would be a nice alternative, and plunks it out. The wiggler guarding it is furious. Bowser asks if Wiggler has a Banzai Bill, which luckily, he does. He tells Bowser to eat the carrot in one minute if he wants the Banzai Bill. After completing the task (with the aid of the bros. in the Gut Check), Bowser reminds Wiggler about the Banzai Bill, but Wiggler seems to forget the previous conversations. Wiggler is furious with Bowser for eating the carrot, and attacks him. After the battle, Wiggler gives Bowser the ammunition, telling him to leave immediately. Bowser starts to head back to his minions, but is stricken with horrible pain. The Mario Bros. finds the source, being a worm-like creature named Durmite, who is causing rampant inside Bowser. A battle emerges, and after defeating Durmite, the worm, now the size of Mario’s foot, takes off. They explore the area, findToadbert, and then watch Bowser learn the Sliding Punch.

Bowser returns to the cannon, and fires the Banzai Bill at his own castle. Midbus, however, lifts the castle over the missile, and lands the castle in Dimble Wood, on top of the unprepared Bowser. Heading to the Rump Command, the Mario Bros. reawaken him with adrenaline, unitentionally growing Bowser to the size of his castle. He even engages it to battle, which significantly damages it enough for Midbus to retreat. Bowser shrinks to normal size, and travels north through the newly created path. Bowser makes his way to the castle, having trouble with Midbus keeping the castle in air. When Midbus fires a giant iron ball at Bowser, Mario and Luigi reboost his arm muscles, allowing Bowser to launch it back to Midbus, knocking the castle back to the ground.

At the castle, he discovers that his minions have been brainwashed by Fawful. He also finds that his military training facility has been turned into Fawful Theater. When he enters the theater, he finds no seats to sit on, and a brainwashed Goomba takes him to a VIP seat. Fawful then appears and announces that Bowser is his special guest, and Bowser is launched into the stage. Fawful brings out Midbus, and then Bowser is forced to battle him in a caged fight. After Bowser defeats Midbus, he is taken by some Boos to a winner’s feast. Here, the Boos force Bowser to eat so much food, that Bowser turns obese and is stuck in the floor from his extra weight.

While exploring the newly opened area, the Mario Bros. find Princess Peach. However, she is kidnapped immediately by Kretins. They chase the creature through the Flab Zone, until it is cornered at a dead end. After battling Alpha and Beta Kretin, they learn the plot of Fawful’s plan, which involves the Dark Star, an evil ancient artifact under Toad Town, and Peach herself. As they try to find a way out, Fawful uses a laser-like machine to pull Peach from Bowser, kidnapping her. Midbus then brings a treadmill, which Bowser falls onto, and literally burns the extra calories. Bowser then sees a sign, bumps into a Bob-omb while reading it, that says "no open fire". The lit Bob-omb then hops into a huge pile of Bob-ombs, and explodes, launching Bowser to the Underground Tunnel.

While making his way through the tunnels, he meets a clan of Monty Moles, who are creating a secret escape route for Bowser connecting to Toad Town Tunnels. With Bowser’s help, they finish the path to the underground Toad Town. Bowser heads through a path that activates a security system, knocking him unconscious. This caused an entrance in the Pipe Yard to open, where the trio are able to exit Bowser’s body. Then find themselves in Toad Town tunnels too, and head to stop Fawful from gaining the Dark Star. When they arrive, though, they are too late. Fawful takes the Dark Star and heads for Peach’s Castle. Just as the bros. are about to enter the castle, barriers are formed by the Dark Star’s power, leaving no entrance to the castle. They then head for Doctor Toadley, searching for an answer to the cure for the blorbs, another unsolved problem. Just as they were in his office, Bowser enters, and engages the bros. in a battle. After they defeat Bowser, the Doctor explains to the three of them that they need to collect the three Star Cures to find a way into the castle. He then tells them that the first Star Cure is held by Durmite, located in Dimble Wood. Bowser overhears this, and heads to Dimble Wood, to get a head start. But the three of them know that Durmite is now in Bowser’s body, and head back to find the first sage.

As soon as they re-enter Bowser, they spot Durmite, which they begin to chase. However, they are soon stopped by a mysterious wall of Boo Blocks, which Durmite ran past. Bowser, on the other hand, is at Bubble Lake, where he runs into a propeller machine that Bowser activates by sneezing (the sneeze, too, was powered up thanks to the Mario Bros.' work). The tower comes out of the water, and lands on Bowser. The trio heads back to the Rump Command, and increase Bowser’s size again. Bowser then attacks the Tower of Yikk, and defeats the moving tower. Bowser returns to normal, and enters the quiet tower. Bowser enters a room, where he finds the ghost of Yikk, who is owner of the tower. Yikk explains his invention, the Boo-ray Machine, that enables various effects on Boo-related things. From the ray light, the Mario Bros. are able to go through the Energy Hold and catch up to Durmite. Then they battle her, in her sage form known as Wisdurm. After she is conquered, she willingly gives the first Star Cure to them. They find the exit, and enter a new area where they activate the Body Slam, allowing Bowser to leave the Tower.

Bowers immediately finds Private Goomp, then asks him if he has seen a Star Cure. Private Goomp tells Bowser about a Star Cure-like object in Bowser’s Vault at his castle. Making his way back to his castle, he uses his new move to explore the remains of his castle. When making it to his vault, he finds that the railroad has been installed through the vault. Worse, the railroad is now property of Fawful, and is used by the Fawful Express. The earlier Monty Moles are now under control of Fawful. Enraged by the treason, Bowser spits fire at the Monty Bros., but they dodge it. The Fawful Express prepares to leave Bowser’s Castle, whilst Bowser is on the tracks, looking for the safe with the Star Cure. As Bowser tries to stop the train from crushing him, he trips, and is crushed into a rock. The Mario Bros. quickly grow Bowser in size, much larger than the train. Bowser takes revenge, and destroys the train. Returning to his vault, Bowser finds the safe the Star Cure is in, but forgot the code. The Mario Bros. journey to Bowser’s Memory Banks, where they search for the missing information. After arriving in the main part of the area, a strange creature scans the bros., and creates blocky duplicates of the bros., to battle them. Once they defeat their counterparts, the creature reveals that it’s the guardian of Bowser’s Memory. It shows the bros. that the safe’s combination has been damaged in his memory, and that the bros. need to repair it. After they solve the puzzle, Bowser abruptly remembers it, and sings it in a short poem. He finally opens the safe, and grabs the second Star Cure. Private Goomp, Sergeant Guy, and Corporal Paraplonk quickly shove Bowser in the safe, saying that Fawful promised them extra rations for their work. Angry at the Star Cure for getting him in this mess, he swallows it. The Marios find it in the Gut Check and head back through the pipe to Toad Town.

Doctor Toadley tells the Marios that the final Star Cure is somewhere above Plack Beach. His intern gives them Birdley to guide them to the last Star Cure. Journeying there, they discover a mountainous path that they never visited before. At the top of the path, they meet the last sage, Chakron, who is also the owner and inventor of the Chakroads. He explains that he would give the Mario Bros. the last Star Cure, but is stuck in his 1000-year pose, and needs help breaking free. After failing to move him an inch, he hints that a special attack in Dimble Wood would help. The trio then heads for Dimble Wood, where they search for the Attack Pieces for Snack Basket. After finding 6 of them and gaining access to a new area, Mario is then kidnapped by a Sockop. Luigi gives and chase, and ends up trapped in a knocked-out Sockop. In a scene reminiscent of Super Mario Bros. 3, Luigi uses this new ability to hop across thorns, and rescue Mario. In the process, Luigi is able to collect the remaining attack parts, and complete Snack Basket. Heading back to Chakron, the three of them use the new move, and succeed. For releasing Chakron from his pose, and giving him a new pose he intends to hold for 100 years, he gives the bros. the final Star Cure.

Mario and Luigi return to Doctor Toadley at the clinic. Taking all three Star Cures, the doctor creates the Miracle Cure, which he sends to cure the blorbs. After completing the process, all the infected Toads are now back to normal. Then the Miracle Cure returns to the Marios, and they take it to the gates blocking Peach’s Castle. Using the Miracle Cure, they are able to break the barriers, and head to the castle.

After searching for an entrance to the castle, they run into a giant pile of trash. As Starlow ponders over why it’s there, Midbus comes in and activates a remote. This causes the garbage to come to life and form the robotic Junker. However, Junker starts malfunctioning and it doesn't obey Midbus's commands properly. Only after Midbus smashes the remote in anger, does Junker finally attack the bros. After receiving enough damage, Junker malfunctions again, rampaging around wildly, freeing Bowser and opening a path in the process. However, Bowser has been in the safe for so long that the small space has given him a horrible back pain. Heading through the secret path to a nearby pipe, the Marios find themselves once again inside the Koopa King. After searching quite a bit, they find Toadsworth inside the Lumbar Nook. He explains that to heal his back, the Mario Bros. must drill into the center of the back. After a very long time (so long that Toadsworth and Toadbert drink some tea to relax), the shock causes Bowser to loosen up his back, enabling him to use the Spike Ball move, and sets off in search of Fawful and the Dark Star.

During his search, Bowser is confronted by giant Piranha Plants that burn him and force him into curling up into a spike ball. The bros. then go to the Chest Station to give impulses that make Bowser fly up so he can fight the Piranha Plants. Not long after defeating them, Bowser finds Fawful and Midbus waiting for the Dark Star to awaken. To aid Midbus, Fawful grants him an ice-based powerup, transforming into Blizzard Midbus to attack. After defeat, Midbus's entire body freezes, with icy air blowing from his nose. Meanwhile, Fawful is absorbing Dark Star’s power, with Bowser punching him before it is complete. Laughing at how that was fun, the awoken Dark Star enters Bowser's body, into the Airway. Mario and Luigi chase it, with it escaping several times, using some of Bowser’s DNA. When they finally trap it into a dead end, Dark Star finally attacks the Marios in battle. Even after defeat, the Dark Star has enough DNA to allow recreating most of Bowser’s body and power for himself. It escapes from Bowser and runs off, with Bowser chasing after him.

Bowser finds Fawful in the conference room, after Bowser defeats Super Peach Castle. The dark power Fawful absorbed allowed him to transform into Dark Fawful. Bowser then fights Dark Fawful, and destroys his body. Somehow, though, he survives as a dark ball of energy. Dark Fawful escapes, but is absorbed by Dark Star. With the two parts back together, Dark Star completes the transformation into Dark Bowser, and escapes through a hidden passage.

Bowser fights Dark Bowser in a quick Spike Ball battle (again provided by the bros.' work at the Chest Station), with Dark Bowser escaping to a tower of the castle. Bowser finds Dark Bowser on the tower high above the Castle. The princess is next to Dark Bowser, unconscious. Dark Bowser states that he will conquer the Mushroom Kingdom, creating an age of darkness. He then traps the citizens of the kingdom within a giant dark hurricane, with Bowser struggling to withstand the force. Starlow then reveals Bowser the truth: Mario and Luigi are within his body, and she asks him not to forget that they are in there to help, but Bowser can barely hear with all the wind in the area. Bowser then states that Dark Bowser will never take over his kingdom, and duels Dark Bowser to an epic final battle. The battle rages on, with Bowser easily defeating Dark Bowser. But, Dark Fawful revives him and turns him giant. Bowser then punches his belly, causing Dark Fawful to be ejected from his body, enabling Bowser to vacuum him up. With Dark Fawful and Dark Star Core inside, the Marios are able to attack all them. After a long battle, the Dark Star Core and Dark Fawful are defeated, leaving Dark Bowser unstable. Mocking him, Bowser punches Dark Bowser until he can’t take any more and explodes. The explosion frees the Mushroom Kingdom from the Dark Star’s influence forever.

Inside Bowser’s body, Dark Fawful is still alive and speaks to the Marios. As he fakes remorse over what he has done, he tries one final attempt to destroy the Mario Bros., and explodes. This explosion actually causes all of the people inside of Bowser to be sent back to the Mushroom Kingdom. The now-conscious Peach, along with other Toads, moves to congratulate the Marios on a job well done. Bowser, confused and angered, realizes that the Mario Bros. were inside his guts. When Starlow tries to calm him by telling Bowser to forget the past, Bowser recognizes Starlow’s voice as "Chippy". When she confirms this, Bowser loses it. The Toads and the Princess flee from the scene, as Bowser promises another epic battle with the Mario bros, and the credits roll.

Afterwards, Bowser is seen lying in a bed at his castle, nursing injuries given to him by the Marios. Private Goomp, Sergeant Guy, and Corporal Paraplonk are there, begging and apologizing for their treason and wanting to rejoin his army. Just then, Birdley comes flying in and drops a present on Bowser’s bed, with Chippy popping out. She came to check on him, afraid that he might attack Peach's Castle again. However, Bowser says he merely wants to fix his castle before doing any more evil. Afterwards, still angry at the truth, Bowser yells at Starlow to leave, which she does. Bowser yells at the three traitors, telling them to go fix his castle. They were speechless, since that meant that they were back in the Koopa Troop. They run off, yelling only thanks, leaving Bowser to himself. Looking around to see if anyone was there, Bowser opens the present, and finds a cake with himself, Mario, Luigi, and Peach on it.

Stats
Each brother and Bowser have their own HP, SP, POW, DEF, and SPEED, as well as STACHE points for the brothers, and HORN points for Bowser. When they finish a battle, they each gain EXP Points and Coins. With enough Experience Points, they can level-up and increase each respective statistic.


 * HP (abbreviation of Heart Points) is the amount of life the player has. When an enemy hits one of them, they lose HP. When their HP reaches zero, they pass out, but can be revived with a 1-Up Mushroom or 1-Up Deluxe. HP can be replenished with a Mushroom, a Nut or a Drumstick (Bowser only).
 * SP (abbreviation of Special Points) indicates how many times Mario, Luigi, or Bowser can use a Special Move. Each attack uses a certain amount of SP, draining the total. SP can only be restored by using Syrup.
 * POW (abbreviation of Power) is how strong the fighter is. The higher their POW stats are, the more damage they will perform.
 * DEF (abbreviation of Defense) is how much damage the player can block from an enemy hit. The higher their DEF stats are, the less damage they will take.
 * SPEED is how fast the player is. The more SPEED they have, the more they can attack an enemy in a given turn.
 * STACHE (Mario and Luigi only) is the most unique of the player's stats. The higher their STACHE stats are, the greater there is a chance of a Lucky Hit, which doubles POW. Also, the player will be more likely to get hits on Scratch Cards with more STACHE.
 * HORN (Bowser only) is exactly like STACHE Points, but is made for Bowser. The higher the number, the more Lucky Hits Bowser will deal and the more hits on Scratch Cards he will win.

Mario and Luigi's Battle System
The battle system with Mario & Luigi is similar to the battles from previous titles. There are now six categories of attack during battle, as opposed to Mario & Luigi: Partners in Time ' s five, or Mario & Luigi: Superstar Saga ' s four. These are Jump, Hammer, Attack Pieces (Bros. Items), Items, Bros. Badges and Escape. The Bros. can defend with their jump and their hammers. The Jump makes Mario and/or Luigi jump to dodge an attack or to counter-attack. The Hammer is used to counter-attack. The music played while battling is the same as the music played during the debut trailer, as seen in the Japanese site.

A new element has been added to battles, a gauge at the bottom of the screen with Mario and Luigi's heads on either end. When Mario or Luigi pulls off an action command, that brother's end of the bar fills slightly. When they meet in the middle, it's possible to use a Bros. Badge move. The effect varies with the equipped badge. The normal effect is to restore 20% of both brothers' HP. Badges can be bought in one of the shops in Toad Town. Some of the badges require that the action commands be pulled off perfectly (EXCELLENT is displayed), and some only need GOOD!. An extra block that appears in the battles can be used to swap the badges that brothers use.

Bowser's Battle System
Bowser has almost the same battle system as Mario and Luigi's, but with a few differences. He has different options: Punch replaces Jump, Fire Breath replaces Hammer and Enemy Attacks replaces Attacks Parts. He doesn't have Bros. Badges. Instead, Bowser has the vacuum ability only after the player advances further through the game. He can then swallow enemies to make Mario and Luigi fight them in his belly, or sometimes he can swallow parts of enemies that can restore his HP, raise defense or attack power, or rescue a Blitty. Bowser's defenses are the Punch and the Shell. Bowser's Punch can counter-attack an enemy. His spiky Shell can hit enemies that try to jump on his head.

Enemy Attacks are special attacks that use members of Bowser's army, which are Goombas, Koopas, Shy Guys, Bob-ombs, or Magikoopas. These attacks require the stylus to perform. These characters need to be liberated to unlock these attacks.

Bowser also has his very own battle system, used when he turns giant. He fights alone against equally-sized enemies during these segments. During these battles, the player holds the DS sideways like a book, and can perform moves with the touch screen and microphone. Sweeping the touch pen across the touch screen will make Bowser execute a Mega Punch against his enemy, while breathing into the microphone will make him breath fire. These battles are turn-based battles.

Bowser Specials
Bowser has 6 Enemy Attacks, 5 of which are obtained via cages.


 * Goomba Storm
 * Shy Guy Squad
 * Koopa Corps
 * Bob-omb Blitz
 * Magikoopa Mob
 * Broggy Bonker

Mario & Luigi Specials
Mario and Luigi obtain these attacks via Attack Pieces found by hitting a Attack Piece Block and other numerous ways.
 * Green Shell
 * Fire Flower
 * Jump Helmet
 * Yoo Who Cannon
 * Super Bouncer
 * Mighty Meteor
 * Spin Pipe
 * Snack Basket
 * Magic Window
 * Falling Star

Items
These are the items that appear in Mario & Luigi: Bowser's Inside Story. Please note that some of the items used in this game have appeared in the previous installments.

Playable

 * Mario
 * Luigi
 * Bowser

Friends

 * Princess Peach
 * Toadsworth
 * Toadbert
 * Starlow
 * Kamek
 * Toads
 * Broque Monsieur, a bipedal creature who seems to be made from ? Blocks.
 * Broggy, Broque's pet.
 * Broque Madame, another bipedal creature made out of ? Blocks.
 * Blitties
 * Three members of Bowser's army:
 * Sergeant Guy, a green Shy Guy with a bag on his back containing a gray pipe and a Magikoopa's wand.
 * Corporal Paraplonk, a red Paratroopa wearing a red bucket on its head and green shoes.
 * Private Goomp, a Goomba that wears blue clothes and seems to look sad.
 * Emoglobin, a species of block-like creatures inside Bowser that give hints and help with minigames.
 * Princess Lipid, who explains Bros. Badges.
 * Yikk, the creator of Tower of Yikk and the Boo-ray Machine.
 * Kuzzle, the guardian of the second Star Cure.
 * Blue Paratroopas, friendly blue shelled Paratroopas.

Enemies
The following is a bestiary for all 55 enemies encountered in the game Mario & Luigi: Bowser's Inside Story. Please note that some of these enemies are variations of a single enemy or were fought in a grouped-battle. For convenience, these variations are listed as separate enemies.

Bosses
The following is a bestiary for all 44 bosses encountered in the game Mario & Luigi: Bowser's Inside Story. Please note that some of the bosses are fought mandatory, with some being optional X forms of bosses. Also note that some bosses involve Bowser to grow giant to fight them. For convenience, these differences in bosses are shown seperated into different groups.

Overworld
While Mario and Luigi adventure through Bowser's Body, Bowser is walking around the overworld. Mario and Luigi can influence Bowser. They can pinch nerves to make Bowser panic. They can also touch Bowser's muscles to give him a power-up. Equally, Bowser can change the course of the Marios' adventure. For example, he can flood them by drinking from a fountain. After a certain point in the game, Mario and Luigi can go to the Pipe Yard and use Warp Pipes to exit Bowser's body and explore the overworld, and then use the pipes to enter Bowser's body again.

Overworld icons have slightly changed. They now display the health of the character. Bowser uses two buttons in the overworld, X to punch, and Y for firebreath. Later in the game, Bowser will learn new moves such as a dashing punch, ground-pounding, and curling up into a spikeball (much like the way he attacked Mario in Super Mario Galaxy). Mario and Luigi use A and B respectively to jump. At one point they will gain hammers. Mario can destroy rocks and crates, while Luigi can hit Mario to make him mini so as to reach previously inaccessible areas. Later in the game, the Marios will learn new moves such as the Spin Jump and the Drill Bros.. They will also encounter items in the overworld that will help them perform moves to reach a goal or an item or etc. The items include a gas pump that seems to be shooting out helium. Mario will fill up with gas, Luigi will grab his legs, and they are then able to perform a floating high jump, somewhat similar to the move found in the first installment of the series. They will also find a Blue Koopa shell that Mario will put on, Luigi will whack him with his hammer, and Mario will hit nearby objects previously inaccessible similar to the move the Koopa companions perform in the Paper Mario series. While Bowser explores a 3-D overworld, Mario and Luigi explore a 2-D world inside Bowser's body, much like a traditional platformer, though they can go into the overworld at any time once the Pipe Yard is available.

The actual overworld is connected just as it was in Mario & Luigi: Superstar Saga, unlike Partners in Time's linear levels. The overworld is up to 4-5 times larger than Superstar Saga's overworld. The map in this game consists of a beach, a forest, a cape, the road to Bowser's Castle, Toad Town, Bowser's Castle, Peach's Castle, Grasslands, a railroad, underground, and a lake. In the Nintendo Power review, it was stated that there are tons of sidequests, much to explore, and plenty to do in the free roam overworld.

In the first two games in the series, Mario and Luigi use a suitcase to store anything they collect in their journey. Here, they use the Star Menu, managed by Starlow, in order to access their items.

Locations

 * Mushroom Kingdom
 * Peach's Castle
 * Dimble Wood
 * Cavi Cape
 * Plack Beach
 * Bowser Path
 * Bowser's Castle
 * Underground Tunnel
 * Toad Town
 * Tower of Yikk
 * Blubble Lake
 * Bumpsy Plains
 * Railroad


 * Bowser's Body
 * Trash Pit
 * Funny Bone
 * Flame Pipe
 * Nerve Cluster
 * Joint Tower
 * Pipe Yard
 * Lumbar Nook
 * Memory Banks
 * Toad Square
 * Pump Works
 * Flab Zone
 * Energy Hold
 * Airway
 * Arm Center
 * Gut Check
 * Rump Command
 * Leg Outpost
 * Nose Deck
 * Chest Station
 * Challenge Node

Differences
While a direct sequel in the Mario & Luigi series, Mario & Luigi: Bowser's Inside Story still has several differences compared to the first two Mario & Luigi games.

Gameplay Differences

 * This is the first Mario & Luigi game to have optional bosses.
 * Unlike Mario & Luigi: Partners in Time for the Nintendo DS, this game makes greater use of the DS's touch controls and microphone.
 * This is the first game in the Mario & Luigi series to have a playable character that is not Mario, Luigi, or their baby forms, other than Toad very briefly during the opening of Superstar Saga.
 * The player can equip Mario and Luigi with pants, gloves, shoes, socks, and accessories instead of just pants as in the first two Mario & Luigi games.
 * Badges have a different function. Bro. Badge moves can be performed with them. This game contains eight badges, which is notably less than the previous Mario & Luigi games.
 * This is the first of the series to have power-ups or other items in the overworld such as the blue Koopa shell.
 * This is the first Mario & Luigi game to have a rank system. This means, if the player gets at a certain level, he/she will go to a higher rank. Ranks for Mario and Luigi are the Mushroom Rank, Shell Rank, Flower Rank, Shine Rank, Star Rank, and the Rainbow Rank. Bowser’s ranks are the Bronze Boss Rank, Silver Boss Rank, Gold Boss Rank, and the Final Boss Rank.
 * Mario and Luigi get the hammers earlier in Mario & Luigi: Bowser's Inside Story than other Mario & Luigi games.
 * The Scratch Card is introduced, allowing the main characters to earn back coins after spending them.
 * This is also the first game where the hammerheads don't fall off in defense when held too long; the bro. just puts it down. Consequently, the hammer can also be held much longer.

Release Differences

 * This is the first Mario & Luigi game to be released in Japan before any other country.
 * This is the first Mario & Luigi game in which the American boxart is the same as Japanese boxart. The European boxart, while not exactly the same, uses the same pictures and background as the Japanese boxart.

References to Other Games

 * Super Mario Bros. 2: During Bowser's battle with the giant Wiggler, the Wiggler sometimes attack by pulling out vegetables, which are the exact same ones that were seen in this game. Also, one of Bowser's brainwashed minions will state that they forgot what Bowser's castle was originally called (before it was turned into "Fawful Theater"), and mistakenly referred to it as "Mouser's Castle".
 * Mario & Luigi: Superstar Saga - Fawful reappears as the villain. The Bros. Attacks from this game were reused, and there was a slight remix of Cackletta's theme song that played in the background after Fawful took over Peach's castle. Lastly, Mario and Luigi battle Dark Fawful inside of Bowser's body, just as they did with Cackletta. Also, the Mini-Mario form returns.
 * Mario & Luigi: Partners in Time - When Mario and Luigi talk to Broque Madame, she tells them stories about the Shroob invasion that took place in the game. Several Shroobs were also seen at Bowser's castle, where they were kept frozen in a cryogenic chamber. If the player chooses to thaw them out, then an optional boss battle with them will commence. During the battle, several other Shroobs, including Elder Princess Shroob can be seen in the background. After the battle, Mario and Luigi told Starlow about their previous battle with the Shroobs, and how they defeated them while they were babies.And while the audience is still in the theater in Bowser's castle, a Shroob can be found sitting in the audience on the top right. Also, there is a badge called the Shroob badge.
 * Super Mario 64 - The music that plays within Peach's Castle when visiting it for the first time is a remix of its theme here.
 * Super Mario Sunshine - One of the brother's rank is called the Shine Rank.
 * Super Mario World 2: Yoshi's Island and Yoshi's Island DS - The Fawful Guy enemy can imitate the attack patterns of both the Woozy Guy and the Glide Guy. In addition, one of its attacks mirrors Yoshi's main form of offense in the game, egg throwing.
 * Dr. Mario - Blue Viruses appear on a poster in Dr. Toadley's office, and in one of a Toothy's attacks.
 * New Super Mario Bros.- Blue Shells make a reappearance. A Mega Mushroom will also occasionally appear during one of Broque Monsieur's attacks during his tutorial.

Trivia

 * This is the first game to have a Boss-Refight or Skill Challenge of the series.
 * This is the first time in the Mario RPG series that a sequel has been released on the same system as its predecessor.
 * The title of the game is a pun on the term "inside story," meaning the "true" tale of an event from the perspective of an insider who participated in the action, as opposed to an outsider who only hears about the event later on. In this case, the game is a literal inside story, as Mario and Luigi have to adventure through the insides of Bowser.
 * The game's European Spanish, European French and Italian name is a pun on the famous novel A Journey to the Center of the Earth.
 * This is the second game where the Mario Bros. battle inside Bowser's body, the first being Mario & Luigi: Superstar Saga, where they battle Cackletta's Soul inside Bowser. It is interesting to note that Fawful (who worked for Cackletta) is fought in a similar way to Cackletta. It is also interesting to note that before both battles take place, the player fights an affected form of Bowser. While Mario and Luigi are sucked into Bowser and Cackletta was inside him, for Fawful it is the reverse; Bowser inhales Dark Fawful and he fights the Mario Bros. inside him.
 * Mario and Luigi can access a cryogenic room in which several Shroobs (including Elder Princess Shroob) can be seen frozen. Starlow speculates that Bowser cryogenically froze whatever Shroobs survived the events of Mario & Luigi: Partners in Time. However, none of the Shroobs (with the exception of Junior Shrooboid, who was kept in a tank for studying) seemed to survive the end of Partners in Time, especially Elder Princess Shroob (as she was turned into a mushroom, eaten by Bowser, possessed him, and was completely destroyed once defeated, as Bowser returned to normal). In addition, given the amount of castles Bowser has ever had, and how many of them have been destroyed, it is unlikely that he actually had this precise castle back when he was Baby Bowser. However, there have been other theories behind this, such as it being a sculpture, the flow of time being altered, or them being frozen in the present and then traveled into the past.
 * There is an alternate ending that happens when the player beats the game over level 40, thus getting the Final ranks for both Bowser and the Mario Bros. In the ending, a voice congratulates the player.

Official Sites

 * Nintendo of America's Website for Mario & Luigi: Bowser's Inside Story
 * Nintendo of Europe's Website for Mario & Luigi: Bowser's Inside Story
 * Japanese Website for Mario & Luigi RPG 3!!!