Max Mushrooms (Japanese: ダイキノコ Dai Mushroom) are an item that was introduced in Generation VIII.
Three clusters of Max Mushrooms can be exchanged for a bowl of Max Soup, allowing a compatible Pokémon to gain a Gigantamax Factor, or revert their status. Feeding Max Soup to Urshifu requires that one comb of Max Honey be added to the exchange.
When used from the Bag during battle, it raises the Attack, Defense, Special Attack, Special Defense, and Speed of a Pokémon currently in battle by one stage each.
In The Winding Path to Greatness!, Allister helped Ash and Goh collect three clusters of Max Mushrooms, which he cooked into a Max Soup that enabled Ash's Gengar to Gigantamax.