Empty Block

An Empty Block (sometimes referred to simply as a Block or a Steel Block ) is a type of block in the Mario franchise that usually appears when Mario, Luigi, and their friends hit a ? Block, an item-holding Brick Block, or a Coin Block, though they sometimes are naturally already in an "empty" state. Empty Blocks are usually brown round-edged cubes with small holes in their sides' corners. In Super Mario World, Empty Blocks have small, closed, angry eyes, but no holes; if the player hits a blue P-Switch, all Empty Blocks turn into coins and vice versa for a short time. Empty Blocks can only be broken by Mega Mario or stronger enemies, such as Broozers, King Bills, and Giant Bowser.

Giant Empty Blocks also appear in Super Mario Bros. 3, Super Mario Galaxy 2, Super Mario 3D Land, New Super Mario Bros. U, and Paper Mario: Color Splash, usually after hitting Giant ? Blocks or certain Giant Brick Blocks. In Worlds 4-2 and 4-5 of Super Mario Bros. 3, they appear naturally, forming part of the levels' structures. Also, in Super Mario 3D Land, Giant Empty Blocks are found in hidden rooms accessed via Warp Pipes (as well as in World 6-3), and are often put together to form sculptures that create 3D illusions.

Rectangular Empty Blocks appear in Super Mario 3D Land, New Super Mario Bros. 2, and Super Mario 3D World as a result of hitting rectangular ? Blocks.

Trivia

 * In the Super Mario Mash-Up Pack in Minecraft, Bedrock is replaced by Empty Blocks.