From the Super Mario Wiki
Mario picking up a Mushroom Block
A Mushroom Block is an item in Super Mario Bros. 2 that is found in Subcon. They are mostly found above ground in castles and World 7. They can be used to defeat some enemies, or stacked up to reach higher areas. They are needed to defeat Tryclyde, Fryguy, and green Birdos, and can also be found in most of the red Birdos' battle rooms. The Mushroom Blocks replace masks used in Yume Kōjō: Doki Doki Panic.
Different worlds have Mushroom Blocks with slightly different patterns, all of which are present in the picture to the left, as follows:
- Top left; Worlds 1, 3, and 5
- Top right; Worlds 2 and 6
- Bottom left; World 4
- Bottom right; World 7
Note that in the SNES version, the Spotted Mushroom Block from the NES was replaced by the plain one (top left).
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