After many sleepless nights, Muriel orders a new mattress. Muriel pays no attention to the grotesque deliverymen who arrive on a sinister horse-bound carriage and hiss at Courage, or the demonic face that appears on the mattress, which Courage witnesses and reacts to with horror. He attempts to warn his owners, but they are clueless to the oncoming danger. Muriel heads upstairs and lies down on the new mattress, locking Courage out of the room. Courage peeks through the bedroom window on a ladder to witness strange green vapors being emitted from the bed and possessing Muriel. She levitates off the bed, and as Courage watches in horror, he falls off the ladder. Courage explains his fear to Eustace, who of course refuses to listen. Courage takes Eustace upstairs where they see Muriel transformed into a demon with fangs and wild, red hair. Eustace and Courage go downstairs, and figure out what to do. Courage goes upstairs to check on her, while Eustace believes the mattress just "gave her nightmares." Courage engages in a thumb war with the demon and loses, fleeing from the room. Courage searches up on the computer how to get rid of the demon. He prints out an incantation for the demon, and after Eustace's failed attempt, getting vomited on by the demon, Courage performs the exorcism and the demon unposseses Muriel. Then, Eustace comes in wearing a haz-mat suit, and tries to perform the exorcism, but the demon possesses him instead. Muriel whacks him with the rolling pin, then she and Courage tie him up in the mattress, which is taken away by the evil deliverymen. The episode ends with Courage lying on Muriel's stomach on the living room couch, as well as Courage saying his last line, "Now this is a bed I can sleep on any day."
- First and only appearance of the Mattress Demon.
- The rats' wagon is a 3D animation.
- Incantation to exorcise a demon: "Hullaballoo, howdy doo! Musty prawns and timbuktu! Hoo! Hoo! Yeltzy bye, hippity hoo! Kick 'em in the dishpan! Hoo hoo hoo!"
- In Queen of the Black Puddle, Eustace's newspaper says "Mattress Special", referring to this episode.
- This is one of the few episodes in which Eustace teams up with Courage to save Muriel without the exchange of money.
- This episode is a spoof of the 1973 film, The Exorcist, frequently called, "the scariest film of all time.," with Muriel as the character of Regan MacNeill, and several other parodies such as sudden vomiting, rising from a bed, head turning completely backwards, and the demon saying, "She's in here, with us."
- Certain scenes of this episode (such as the demonic head-spinning) may be censored in some countries.