Boo Blocks are a type of Boo that appear in Super Mario World on the Super Nintendo. Appearing in the Chocolate Island Ghost House, these Boos turn into stone blocks when Mario is looking at them. When Mario looks away, they turn back into Boos and float towards him.
Boo Blocks cannot be defeated with any power-up, although they also shouldn't be. Boo Blocks are required to complete the Choco-Ghost House as the exit door is located on a high platform that cannot be reached conventionally. Mario must lure the Boo Blocks towards him, turn around to make them turn to blocks and then use them as footholds to reach the exit platform.