From the Super Mario Wiki
A Zombie Shroom is an enemy that appeared in Super Paper Mario. Sometimes Mario, Princess Peach, Bowser or Luigi will find a Mushroom or a relative item in a ? Block that instead immediately turns into a Zombie Shroom, moving extremely fast in the same pattern as a normal mushroom and dealing two damage with each hit. A single jump defeats it as it only has 1 HP, causing it to drop five coins. There is a stronger variant of this enemy, the Ghoul Shroom, which is gray.
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