The Mushroom Trap is a cut trap in Dungeon Keeper. It was in (or at least intended to be in) the game as of early 1996.[1]
Given how one of the icons depict this trap, and the fact that certain mushrooms are poisonous to humans, it is possibly an early version of the Poison Gas Trap. If so, it is plausible that the fact that there are several species of creature in the game is why it was changed. The mobile Dungeon Keeper game has a Poison Trap that looks like some mushrooms; whether this is coincidence is unknown.
