The Mattress Demon is an evil spirit that resides with a mattress. He makes his presence known by manifesting a face to frighten Courage. He later takes possession of Muriel, changing her appearance to green skin with wavy orange hair and a deep, male, demonic voice. Courage and Eustace spend most of the episode trying to get rid of the evil spirit. Courage uses the incantation to drive the spirit out of Muriel. Minutes later, it possesses Eustace. Muriel knocks him out and orders the mattress to be taken back.
- The Mattress Demon is not part of the "Ball of Revenge".