Demons are a species that first appear in "It Came from the Nightosphere." The only demon who appears in the episode is Hunson Abadeer, who is Marceline's dad. Other demons appear in "Return to the Nightosphere," when Finn and Jake explore the Nightosphere. Demons usually have a humanoid shape and most of them look completely different from one another. Some of them are friendly, and others are very serious and strict. Only a few demons are truly evil.
The Boat Demon is shown in "Return to the Nightosphere," where he's shown rowing a boat on the heads of the demons in line. He tells Finn and Jake who the Teller is, claiming he only likes rowing on demons' heads. He seems to be loosely based on a psychopomp, such as Charon from Greek mythology.
The Teller is a demon appearing in "Return to the Nightosphere." His job is to give tickets to visitors who wish to see Hunson Abadeer, similar to the "Take a Number" system used in some businesses. He gives Finn and Jake a paper that reads "42,000,000" and explains to them that once the number on the paper matches the one on the door, they'll be allowed to see Abadeer. However, this just leads them to another line. The ticket number given to Finn and Jake could be a reference to The Hitchhiker's Guide to the Galaxy, in which 42 is said to be the answer to the ultimate question of life, the universe, and everything.
The Big Demon appears in "Return to the Nightosphere," shown in line to see the Teller. When asked by Finn how long has he waited in line, he starts crying. When the two try to stretch in front of him, he threatens to kill them. He is later seen in "Daddy's Little Monster," in line before the Ab Demon. After being asked by Hunson Abadeer (Marceline wearing the Nightosphere amulet) whether he wants pain, pleasure or weird punishment, he chooses pain, thinking it will bring him something good, but instead he gets half of his body disintegrated.
The Line Demon is a character shown in "Daddy's Little Monster," waiting in line. He catches Finn and Jake trying to cut in and manages to put them back in their starting place. He tries to get back in line, but he's reminded by another demon he got out of the line himself.
Weird Punishment Demon
The Weird Punishment Demon is one of the demons shown waiting in line. When questioned by Hunson Abadeer (Marceline wearing the Nightosphere amulet) whether he chooses pain, pleasure or weird punishment, he answers pleasure, but instead, he gets the weird punishment: vomiting bananas.
The Ab Demon is one of the demons that appeared waiting in line to meet Hunson Abadeer. He tries to leave before he gets hurt like the "cowering speck" before him, but fails. When asked by Hunson (Marceline wearing the Nightosphere amulet) whether he wants pleasure, pain or weird punishment, he declines all of these suggestions. Marceline asks him if he wants abs, which he accepts, so Marceline turns his face into a six-pack.
Charlotte was a young demon who shortly appeared in "Return to the Nightosphere." She was seen playing with tiny demons, and holding one in her hands. Her dad told her to stop playing with the smaller demons, saying that they are "dirty and stupid."
Charlotte's father appears in "Return to the Nightosphere." He warns his daughter not to play with the smaller demons because they are "dirty and stupid." He was blasted by a ray from the cloud, turning him into several smaller demons.
Demon Pig is a demon who appears in "Ocarina" and "Summer Showers". He is a tenant in the Tree Fort when Kim Kil Whan rents it out. He also attends the play Summer Showers in the episode of the same name.
Shadow Slender Demons are demons which appear in "Jermaine" where they crowd around outside Joshua and Margaret's house trying to get in, but are blocked by a salt barrier. They desperately try to obtain things from inside the house but go away at the end as the house burned down.
- Hunson Abadeer
- Nightosphere Jailer
- The Teller
- Half Monster Demon
- Finn (temporarily)
- Shadow Slender Demons
- Grass Demon
- Marceline (former human/demon hybrid; currently a vampire/demon hybrid)
- Farmworld Marceline (alternate timeline, human/demon hybrid; deceased)
- Marshall Lee (fictional; vampire/demon hybrid)
- They were first mentioned at Wondercon 2012.
- Most of them were designed by Andy Ristaino.
- The demons in the Nightosphere excrete bananas from various orifices.
- It is shown that Demons have a little hatred to the rules of the Nightosphere.
- There may be different 'species' of demons as most are different in appearance, but a few are very similar, such as Charlotte and her father.