There are a number of ways to cure this condition: Generally it’s the mushroom enemies in Earthbound that cause this condition, such as Ramblin’ Evil Mushroom (which is encountered outside Twoson), and the Shrooom! boss outside Rainy Circle.
Mushroomized Effects
Effects of Mushroomized include remapping your controls in the overworld and characters ignoring commands in battle, and sometimes even attacking other party members. Having your controls remapped is annoying. And it keeps changing periodically as you play, meaning just as you’ve learned the new directions they’ve soon changed to new ones. Far worse than this though is the in-game effect: The affected character will attack other party members, heal enemies, and generally be a pain. The prompt “(character name) is feeling funky!” will precede the Mushroomized character’s confused attack. But it’s worth mentioning that there’s also a chance of Mushroomizing an enemy if a Mushroomized character casts a PSI ability on them. Characters affected by Mushroomized will also have a mushroom on their head in the overworld.
Healing Mushroomized (All Methods)
The easiest way to get rid of mushroomized is to visit any hospital in the game and seek out the blue-haired healer. These guys will offer to buy the mushroom off the head of each affected party member for $50 a piece. Alternatively, you can also visit Peaceful Rest Valley and look for the girl foraging for mushrooms. She’ll be located just after the area with the cave. She will offer you the same price to purchase the mushrooms from each character affected. And finally, as a third option you can visit the pink hot springs in Saturn Valley or Tenda Village. These hot springs will also remove the mushrooms. Unfortunately you cannot heal Mushroomized with PSI abilities. There is also a 4th method of removing the Mushroomized condition, but it means killing off the character that’s affected. So we’ll leave that decision up to you.