From the Super Mario Wiki
Rotating Blocks, also known as Flip Blocks and Turning Blocks, are yellow, eyed blocks found in Super Mario World and the Super Mario World style of Super Mario Maker. When hit from below or the sides, they briefly spin around, allowing Mario to pass through them. Super Mario can destroy them with a Spin Jump from above. Chargin' Chucks can also destroy Rotating Blocks by charging into them. Also, enemies such as Koopa Troopas and Galoombas may hide in Rotating Blocks, and break out to attack Mario once he approaches him. They replace Brick Blocks from previous Super Mario games, and share most of those blocks' attributes.
Rotating Blocks appear in the Super Smash Bros. series in Melee's Yoshi's Island stage (in Super Smash Bros. Melee, Super Smash Bros. Brawl, and Super Smash Bros. for Wii U), and in the Super Mario World style of the Super Mario Maker stage (in Super Smash Bros. for Nintendo 3DS / Wii U as DLC), working as they originally did, though they are 3D in Yoshi's Island (they turn 2D when rotating).
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