Vanishing Block
From the Super Mario Wiki
A Vanishing Block is a block that appears in Super Mario Advance 4's World-e. It appears one level, Tanuki Suit no Himitsu. Though the block is entirely solid and inert, it is invisible under normal circumstances. To make it visible, Mario must use the Tanooki Suit's power to become a statue. A Tanooki Suit is hidden in the level for this express purpose. There are many puzzles in the level that combine Vanishing Blocks and Grey Brick Blocks.

