Demonius appears alongside other demons of Hell when Satan tells about a party that he is having on Earth on Halloween night. He tells Satan that he must "be wary" because he invited so many celebrities that there aren't enough wristbands for people in Hell. He later suggests a donut machine after Satan is told that P. Diddy had taken his ideas for a dessert for the party. Later on at the party, he is seen dressed up as Captain America when one of the hotel staff members tells him that Satan's Ferrari Cake never showed up. He then decides to replace the Ferrari Cake with an Acura Cake, much to Satan's anger.
Demonius has a head with a bald top and long gray hair on the sides and gray eyebrows. He has a large scratch on his left eye, making it look different from his other eye. He wears a large black robe that obscures his feet. He also has very sharp fingernails and pale wrinkly skin.