Ultra Mushroom is one of the best HP-replenishing items that you can find in Paper Mario: The Thousand-Year Door. Because it restores a high amount of HP, they're much rarer than their Super Mushroom counterpart and cost well over 100 Coins. However, the latter half of Thousand-Year Door features stronger enemies and bosses, and while you can recover HP with the Special moves Sweet Treat/Sweet Feast, you'll likely want to save your Star Power in case you find yourself in a pinch. Depending on how you're leveling up Mario, an Ultra Mushroom can fully restore his or his ally's HP, making it a worthy item to add to your inventory.