After escaping the in the previous episode, Finn and Jake realize they accidentally left Marceline the Vampire Queen behind. Upon returning to rescue her, they discover she has been transformed into a massive, chaotic demon by a mysterious amulet.
This episode is significant for introducing the Nightosphere Amulet as the source of Hunson Abadeer's immortality and demonic powers. [S4E6] Daddy's Little Monster
Hunson reveals he tricked Marceline into wearing the Nightosphere amulet, which fills the wearer with "chaotic evil," because he wants her to take over the family business of ruling the underworld. After escaping the in the previous episode, Finn