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.
- Mattress Demon was one of 17 villains who were not part of the Ball of Revenge. The others were Fred, Schwick, Velvet Vic, Mondo, Jeeves Weevil, Fishsionary, Evil Empress, Bluff, Big Bayou, King Ramses, Dr. Gerbil, Elisa and Eliza Stitch, Benton Tarantella, King of Flan, Errol Van Volkheim and Mad Dog.