The Moon was a vampire and a member of the Vampire King's court.
Marceline fought The Moon centuries ago when she was on a mission to protect the remaining humans from vampires. The encounter was difficult thanks to The Moon's regeneration abilities and her "hide and seek" style of defense. Marceline managed to defeat her and gain her healing powers.
The vampires are resurrected after Princess Bubblegum removes Marceline's vampire essence from her. After a short period, the Vampire King and his court manifest. While the other members of the vampire court debate what to do, The Moon calmly listens. When it appears that disagreements are breaking up the vampire court, The Moon parts ways with the group to go be off on her own. She heads towards a lake, dropping moon pearls as she leaves.
Finn and Jake hunt for The Moon in daylight with the hopes that Marceline can re-absorb her healing powers to cure the fatal poison she is inflicted with after a battle with The Hierophant. They follow her pearl trail to a boathouse, where they find her sleeping in an urn. They soon discover that neither simple stakes nor the sun can cause permanent harm due to her rapid healing powers. When night falls, The Moon pursues them with alarming speed to Peppermint Butler's lab in the Candy Kingdom. She easily defeats Marceline's friends with her paralysis powers, and manages to open the lock to the safe Bubblegum and Marceline were hiding in by merely shouting "pig" at it repeatedly. Peppermint Butler finally stuns her with a gigantic stake, allowing for Marceline to soul-suck her powers and cure herself from The Hierophant's poison.
The Moon is calm, quiet, and passive most of the time. She is filled with mystery and she takes advantage of this, to look as creepy as she can.
When she hunts, however, she reveals a malicious and dangerous persona, reflecting a mysterious aura. Incredibly twisted and scheming, she now talks in a deep, demonic voice and speaks in riddles and metaphors, causing a sense of confusion and fear in her prey. She's also more openly violent and angry. The Moon seems not to like talking, as shown when the other vampires were arguing and she remained silent.
The Moon has the appearance of a short, stout woman with long black hair and a serene expression. She wears a dark gray dress, a lighter gray poncho, and a golden pendant decorated with a crescent moon. Compared with the other vampires, she looks mostly human except for the bat ear growing out of the center of her forehead. The ear expels glowing blue orbs called Moon Pearls. She has green catlike eyes and sharp teeth.
- "Everything Stays"
- "Vamps About"
- "May I Come In?" (mentioned)
- "Take Her Back"
- "Ketchup" (mentioned)
- "Orb" (In Jake's dream)
Powers and abilities
The Moon is a natural vampire, who like the rest of the Vampires in the court has a set of unique abilities, that include such:
- Self-Healing: The Moon has extremely powerful self-healing abilities, more powerful than those exhibited by Marceline as she is shown regenerating from sunlight and sustaining a healed form under constant bombardment, whereas Marceline may die. This is ability is seen in both "Vamps About" and "Take Her Back." Her healing power even allows her to survive being staked in the heart.
- Moon Pearls Production: She leaves behind moon pearls (spherical items of an unknown substance) as she moves, as seen in both "Vamps About" and "Take Her Back."
- Speed: The Moon is able to run incredibly fast, due to an enlarged number of legs under her dress, as seen in "Take Her Back." However, with this she has a connection with the moon, as she will follow her prey until exhaustion, and keep the same distance without catching up or stopping, just like the moon itself.
- Muscle Paralysis: She can induce muscle weakness in her enemies, causing them to collapse at her feet, through psychic powers. With the latter power, it may be that her malicious form terrifies her foes into submission as it seems that she yelled at a lock until it opened of its own will.
- Lunar Relationship: The Moon has a strange affinity with the moon. It is implied that one is safe from her as long as they are out in the moonlight, and in many frames she's replaced by the actual moon and its light. One could assume that she gets most of her power from the moon, and Finn, due to what she's stated, is unsure if she means that she actually is the moon itself.
- Flute Player: In "Vamps About" after being formed, she can be seen playing the flute.
- She is named after the eighteenth trump or Major Arcana card in traditional Tarot decks. The Moon card represents dreams, deception, and illusions. Similarly, Moon, who spends much of her time sleeping, appears deceptively innocent until her more malevolent side is shown. In the reversed position, the card can represent confusion, which ties into Finn and Jake's misunderstanding of Princess Bubblegum's orders ("You guys take her back" vs "You guys stake her back").
- Marceline describes her as "fighting a cutting board" due to her regenerative powers.
- Jake describes her as looking like "if an anthill was a girl."
- She is seen playing a flute when she was revived in "Vamps About."
- The Fool calls her "Backwards Egg."
- None of the other members of the Vampire King's court is ever seen directly speaking to The Moon, let alone acknowledging her presence, except for, rather ironically, The Fool. Only the Fool, The Hierophant and Marceline are ever shown speaking about her existence in the Court, and Marceline herself only references her name once, in a fever dream, when she mistakenly remembered The Moon as her most recent encounter instead of The Hierophant fight.
- In Adventure Time: 2015 Spoooktacular comic, The Moon has mentioned The Fool by saying, "My fool of a brother has told me about you," when talking to Marceline. Either The Fool and The Moon were once siblings or it is a nickname to call another member in the vampire court "sister" or "brother" referring to The Hierophant calling The Moon, "Sister Moon."
- Given the numerous references to music in the series, her nickname is most likely a reference to the song "Brother Wolf, Sister Moon" by The Cult. This is further supported by The Hierophant taking on a wolf-like form.
- It is theorized that the bat ear growing out of The Moon's forehead is her actual ear.