Having faced the denizens of the Bean Kingdom, and traveled across time and space to rescue the Mushroom Kingdom and its Princess, Mario and Luigi face their biggest adventure yet: Bowser's innards.

Mario & Luigi: Bowser's Inside Story will once again feature a wacky and quirky story. This time around, the citizens of the Mushroom Kingdom suffer from The Blorbs, a disease that makes them grow large in size and turn into balls. During a meeting in which Peach, Mario and Luigi discuss the solution to this epidemic, Bowser attacks but is quickly defeated and sent by Peach and Starlow to Ekubon's Forest. In this forest Bowser encounters a Lucky Mushroom, which is really a Vacuum Mushroom trap set up by Fawful. When Bowser consumes the mushroom he begins to inhale everything, including Peach, Mario and Luigi. Now inside his nemesis, Mario learns that in order to continue his adventure he and Luigi must take control of Bowser and save the Mushroom Kingdom.

Gameplay in Bowser's Inside Story will be similar to the previous titles. It is once again be a turn-based RPG, now featuring 6 attack commands: Jump, Hammer, Attack Parts (items that can be used in battle), Bros. Badges, and Escape. A new addition to the Mario & Luigi formula is a gauge at the bottom of the screen, one for each brother. When each character performs an attack, the bar fills up a little. When both bars meet in the middle the brothers can perform a Bros. Badge Move.

Badges will once again play a big part in gameplay. Badges can alter a character's stats when equipped, and can be bought at the shops in Toad Town. Some of the Badge Attacks are required to be pulled off exceedingly well (this is indicated by the words EXCELLENT on screen) for maximum effectiveness.

In addition to the Mario brothers, players can also control Bowser. Playing as Bowser is similar to using Mario and Luigi, except tailored to fit his attacks. Bowser can punch, use his fire breath and use enemy attacks. Instead of Bros. Badges, Bowser can use his new vacuum ability. He can suck in enemies, which in turn become enemies for Mario and Luigi to battle inside of Bowser. Some enemies can even replenish Bowser's HP during battle. When Bowser uses his enemy attacks, some of his minions (Goombas, Koopa Troopas, Shy Guys, Bob-Ombs, Magikoopas, etc.) will do the dirty work.

The battle control scheme changes completely when Bowser encounters enemies of his own size. Players then turn the DS on its side like a book, controlling Bowser using the touch screen and microphone. Sweeping the DS stylus across the touch screen will make Bowser do a super punch on his enemy, while blowing on the microphone will make him use his fire breath.

Outside of battle, exploration remains similar to previous titles. Players can now explore the inside of Bowser's body, controlling him by attacking certain points inside him while he is exploring the overworld. For example, players can make him panic by pinching his nerves, while attacking his muscles give him a brief power up. This becomes crucial during exploration, as the Mario brothers use Bowser to open new passages and solve puzzles.

Bowser's Inside Story will feature some elements different from the previous Mario & Luigi titles. This will be the first Mario & Luigi game to use the touch screen and microphone to execute commands, a feature not present in Mario & Luigi: Partners in Time. The brother's equipment has also been expanded; players can now equip the brothers with gloves, shoes, socks and other accessories. This will be the first Mario & Luigi title to feature optional bosses, something less experienced players may appreciate.

The Mario's Bros. inside story will finally be told when Nintendo releases Mario & Luigi: Bowser's Inside Story on September 14.