Amanita

Amanitas, known in Japanese as Popin (ポピン), are mobile fungus enemies found in Super Mario RPG: Legend of the Seven Stars. They live in the Forest Maze and disguise themselves as common curative Mushrooms (which are plentiful in the forest). When an unsuspecting mushroom gatherer approaches a concealed Amanita, the fungus creature will reveal itself and attack. However, not all Amanitas disguise themselves; some move freely on the ground. One Amanita even hides in an underground bush and ambushes travelers that pass by.

In battle, an Amanita attacks by twirling into one of Mario's party members. Aside from its regular attack, the Amanita can use the special attack known as Sporocyst to turn others into fungi. As a Mushroom, a party member cannot attack, use items, defend, or even move. The only positive side effect of being turned into a Mushroom is that a party member's HP will slowly recover. Since Amanitas are fungi, they may be distant relatives of Toads and Goombas.

Trivia
The Super Mario RPG Amanita's behavior of disguising itself as a helpful mushroom is probably a reference to this.
 * Amanita is a real genus of fungi, many members of which look similarly to the Mario series enemy and one of which the Super Mushroom in Super Mario Bros. was based off of. Although it includes many toxic species, it also contains species which are commonly eaten in some cultures.  Those looking for an edible species could be poisoned when they confuse two similar looking species.
 * Another mushroom-like enemy also called "Amanita" appeared in Chrono Trigger. Both Super Mario RPG and Chrono Trigger were developed by Square for the Super Nintendo.