Magic Window

Magic Window is a secret Attack Piece used in Mario & Luigi: Bowser's Inside Story.

When using this special technique, Mario and Luigi jump into a window, which teleports them close to a random opponent. As Mario or Luigi jump out of window, the player has to decide which button to press: A, B, or both of them. This attack will cost eighteen SP to use.

This is unlocked by defeating the optional Shroob boss. Interestingly enough, the shape of the window itself seems to be modeled after the Shroob Empire symbol used in the last game.