Odd Mushroom is a troll found in the troll town of Weiss, who is an inventor and also Mother's advisor. Unlike most trolls, Odd Mushroom is extremely intelligent and speaks perfect common tongue, like the Troll father, troll mother and troll child. He values skills over combat, having more affection for Mother's daughter Snowflake due to being his pupil and her quick learning capabilities.
He documented ways to use salt found in the mines beneath the town (te, urt and efh) to provide different boosts in Weiss fire notes, some of which were lost by the book becoming damaged.
During Making Friends with My Arm, he is mortally wounded by Mother after discovering he was tricked into believing the Wise Old Man was dead. He succumbs to his wounds in prison shortly after instructing the player to find his notes.