Ramblin' Evil Mushroom
Ramblin' Evil Mushrooms are enemies in EarthBound that attack by spreading spores on Ness and his friends. The status they inflict is Mushroomization, which causes a mushroom to sprout on their heads which overtime reverses and rotates their controls on the overworld, which is referenced by their effect in Ultimate. Similar variants of this enemy appear in both EarthBound as well as Mother 3.
As an item
The Ramblin' Evil Mushroom walks around the stage, waiting for players to pick it up. Should they do so, they can attack with its spores in a manner similar to the Fire Flower's flames. Any fighter hit with its spores will have a small mushroom appearing on the character's head, similar to the Flower effect. Once the opponent is hit by enough of the spores (visualized by a larger mushroom, which will begin to emit spores), the affected fighter's controls will become reversed. The mushroom cannot be planted on fighters equipped with a spirit with an "Irreversible Controls" effect. If the Ramblin' Evil Mushroom is attacked, it will spray spores around itself, damaging anyone around it.
The Ramblin' Evil Mushroom also appears as a Spirit.
In addition to the above, equipping the Toadsworth, Grim Leecher or Bellossom Support Spirits will give the player a Ramblin' Evil Mushroom at a start of a match.