The Chromatic Demon is a tanar'ri demon imprisoned in Watcher's Keep. He was forced to help servants of Helm in securing the Imprisoned One in the Keep. To protect the Keep, the Helmites gave him a key to get to the third level whilst also trapping him inside a magical cage. First, four scepter keys would have to be collected to free the demon, and then the demon would have to be killed to get the key, hence guarding the level.