Yoo Who Cannon is a Special Attack that appears in the game Mario & Luigi: Bowser's Inside Story.

When using this attack, Mario and Luigi will briefly appear in eight barrels on screen; the player has to remember where they are. After a barrel rises, the player has to press A Button for Mario or B Button for Luigi, depending on which brother was in the cannon, the player has to press the correct button to damage the enemy before the fuse reaches the barrel. If the wrong button is pressed or if the player takes too long, the other barrels will be destroyed, and it will do less damage and stop the attack. It costs seven SP to use this attack. After teaching Mario how to use Blue Shells, the Blue Paratroopas will give Mario and Luigi the 10 Attack Pieces required to use this move. It, Green Shell and Snack Basket are the only Attack Pieces that are required for the game.

This move is available for use in the Challenge Node. It becomes trickier when remembering the order becomes shorter.


  • Its name is a pun on the two words, interjection "Yoohoo!", and exclamation for waving and the word "Who?" questioning who is in the barrel.