Attack Piece Block
From the Super Mario Wiki
Attack Piece Blocks are blocks from Mario and Luigi: Bowser's Inside Story with the letter "A" in them, most likely standing for "attack". Attack Piece Blocks are scattered throughout Bowser's body and in places outside Bowser such as Dimble Wood. Blocks inside Bowser's body look two-dimentional, while blocks in the 3D outside world are also 3D. There are ten Attack Piece Blocks in almost every area; they will give Mario and Luigi an Attack Piece if struck. Hitting all ten will give the bros. a new Special Move. Sometimes Mario and Luigi can find several of these blocks all at once. Once in a while they can get all ten at once. Bowser can not strike these blocks.
