Yoo Who Cannon

Yoo Who Cannon is an Attack Piece that appears in 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 the "A" or "B" button, depending on which brother was sitting there. If the wrong button is pressed, the attack immediately fails. This costs seven SP to use this attack. After teaching Mario how to use Blue Shells, the Blue Paratroopas will give Mairo and Luigi the 10 Attack Pieces required to use this move.

It seems possible that this attack was derived from the launch barrels in the Donkey Kong universe.