Skeleton Princess (also known as Zombie Princess) is the ruler of the Boneyard Kingdom and first appears in the Ice King's Imagination Zone in "What is Life?" She later appears in "Loyalty to the King" as one of the princesses who is interested in the Nice King (Ice King's alter ego). She does not say much and seems to like biting things, as seen in "Loyalty to the King," when she repeatedly bit the metal bars of the cage she was in. She is also seen with Purple Princess and Hot Dog Princess walking in a circle with Nice King.
She appears again in the episode "Princess Monster Wife," where she is one of the princesses that Ice King likes a particular body part of as he steals her left leg.
Skeleton Princess makes another brief appearance in "Princess Potluck," in which Finn either does not recognize or does not remember her and refers to her by "heyyyy, youuu." In "Princess Day," she is considered to be a registered princess.