Rotten Mushroom

Rotten Mushrooms are purple, skull shaped mushrooms that appear in Super Mario Maker 2. They replace 1-Up Mushrooms when the night mode is activated, but only for the Ground course theme. Unlike most mushrooms, Rotten Mushrooms actively pursue the player; if they are under the Super Star's effects, however, Rotten Mushrooms will evade them. Touching a Rotten Mushroom powers down the player, similar to a Poison Mushroom, making it a hazardous obstacle. Their skull-like design and role as an "evil" counterpart to "good" mushrooms makes them comparable to Poison Mushrooms, Zombie Shrooms, and Ghoul Shrooms.

Two Story Mode levels posted by World-Renowned Chef imply that Rotten Mushrooms are Super Mushrooms that have rotted over time and became vengeful.