Stool is a Myconid sprout captured by Sarith Kzekarit. Stool is lonely and frightened, wanting only to return to its home in Neverlight Grove. If befriended by the characters, Stool gladly offers to guide them to its home, promising them sanctuary with its folk, although it isn't aware of the dangers posed by Zuggtmoy's influence on the Myconids.
Stool uses rapport spores to establish telepathic communication with other creatures, and it does so to communicate with characters who are kind and friendly toward it. The Myconid will also help establish communication with Underdark denizens with whom the characters don't share a language. Once it becomes attached to one or more of the adventurers, Stool behaves somewhat like an enthusiastic and curious younger sibling, sticking close to the characters and asking all kinds of questions.