Half Monster Demon

The Half Monster Demon is a character who appeared in "Return to the Nightosphere." After Finn and Jake asked him how they can talk to Hunson Abadeer, he brought them over to the "line" that leads to The Teller, since he would be able to help them. His organs are "habitable," so anyone who uses him to transport somewhere can survive without being digested.

Appearance
It looks as a long, pink cylinder cut in half and, therefore, all its organs are exposed. It has long and thin legs, one big eye and its tongue is always out of its mouth.

He somewhat resembles a Ghast from Markus Persson's Minecraft

Abilities
He can levitate if he needs to move fast. The demon also communicates telepathically rather than speaking aloud, though its telepathic voice appears to have a minor speech impediment.

Quotes
"The Teller can help you. Get in my flippin' belly and I will transport you. My insides are habitable. You will not be digested."