Vampires

Vampires are a little-known species in Adventure Time. Their self-proclaimed queen is Marceline.

Marceline has demonstrated numerous powers, including levitation, pyrokinesis, telekinesis, invisibility, and necromancy, as well as the ability to shape shift into numerous monstrous forms, including a bat, a wolf, a reptilian creature, or a tentacled monster. Some of these powers, including levitation, invisibility, shapeshifting, rapid regeneration and telekinesis, seem to be the unique powers of specific vampires, which were absorbed by Marceline after she slew them.

Unlike, it appears vampires in the Adventure Time universe are capable of sustaining themselves on "shades of red," such as the color in strawberries, and are not limited to surviving on blood. However, Marceline is the only vampire who has been shown willing to live this way.

Vampires are far stronger than a normal person and have an evolved sense of smell. They also possess marvelous fighting skills. So far, they have been shown to be vulnerable to sunlight, garlic (possibly), and stakes, which are classic vampire weaknesses. Marceline states "Vampires can't beat Ghosts; it's like a thing," in "Heat Signature."

Powers
The following powers have been demonstrated by vampires:
 * Agelessness - Vampires do not age, and are immortal unless slain.
 * Levitation - Originally possessed by The Fool and absorbed by Marceline before she became a vampire.
 * Invisibility - Originally possessed by The Empress and absorbed by Marceline before she became a vampire.
 * Hypnotic Eyes - This power appears to be exclusive to The Empress. It either was not absorbed by Marceline or she simply has not had any reason/desire to use it.
 * Shape-shifting - Originally possessed by The Hierophant and absorbed by Marceline before she became a vampire. The Moon also demonstrates shapeshifting powers to a lesser degree, being able to make her face more menacing and seemingly grow additional legs to run.
 * Regeneration - Originally possessed by The Moon and absorbed by Marceline before she became a vampire, although not as rapid as the Moon's as she is still vulnerable to sunlight while the Moon is invulnerable to it.
 * Telekinesis - Originally possessed by the Vampire King and absorbed by Marceline when she staked him at the same time that he bit her and turned her into a vampire.
 * Vampire conversion - The Vampire King can "turn" people and animals into vampires with his bite. It is not known if this is a universal vampire trait. Princess Bubblegum did not become a vampire when Marceline bit her in Red Starved, however it's possible that candy people might be immune to vampirism, or that conversion might be something a vampire needs to do on purpose and not an automatic consequence of the bite. In Heat Signature, Marceline indicated that she can turn humans and perhaps even dogs, but it cannot be confirmed whether she was being sincere or joking here.
 * Necromancy - So far, this power has only been demonstrated by Marceline. It is not known if this is a vampire power.
 * Hydrokinesis - So far, this power appears to be exclusive to The Vampire King. It is unknown if Marceline acquired this power as well.
 * Pyrokinesis - So far, some type of control over fire has only been demonstrated by Marceline. It is not known if this is a vampire power. Also, given that she only activated some candles, it's possible this was telekinesis (via friction) rather than pyrokinesis.

Weaknesses
Vampires are burned by sunlight and garlic, and a stake through the heart will reduce them to dust. Additionally, the Hierophant has many of the "old school" vampire weaknesses, including the inability to enter houses unless invited in.

Hierarchy
As mentioned by the Empress, the vampire hierarchy system revolves around a hive that consists of lesser vampires referred to as "minions," under the command of a master vampire, such as the Empress herself and other members of the Vampire King's court. All the vampires are ruled by the Vampire King until he and most if not all his kind are wiped out by Marceline, who herself was bitten by the king and as the result she herself became the last surviving vampire, claiming the title of "Vampire Queen".

Additionally, The Hierophant was an "old school" vampire, constrained by "old timey" vampire rules, including the inability to enter a house uninvited. When he was knocked over and fell into a house uninvited, it reduced him to dust and bones. In "Heat Signature" it is claimed by Marceline that vampires cannot beat ghosts.

Notable Vampires

 * Marceline
 * Marshall Lee (Marceline's in-universe fan-fictional 'gender-swapped' version)
 * Keila (comic only)
 * The Vampire King (former vampire, cured and became a lion)
 * The Empress (deceased, killed and absorbed by Marceline)
 * The Hierophant (deceased, accidentally killed by Crunchy and absorbed by Marceline)
 * The Fool (deceased, killed and absorbed by Marceline)
 * The Moon (deceased, killed by Peppermint Butler and absorbed by Marceline)

Trivia

 * Marceline is truly the queen of vampires, because she appeared at the meeting of Ooo Royalty in "The Duke." She seems to have given herself this title after defeating the Vampire King, albeit while also being turned by him. In fact, she is the only remaining vampire known.
 * Marceline's father was stated by Adam Muto to be more of a demonic creature, which leads many to consider him not a vampire. He has shown no evidence of any vampire-related abilities.
 * Marceline has bite marks on her neck in her current state, but they were not visible on her neck as a child ("Memory of a Memory") nor on the neck of Farmworld Marceline, who is visibly older. This was later shown to be because she was bitten by a vampire after splitting with Simon Petrikov. Her turning did not occur in the Farmworld reality, where it was shown that although her half-demon blood slows her aging (she lived at least 1003 years), having vampire powers is chiefly why she seems not to age.
 * With the exception of Marceline and the Vampire King, all currently known vampires seem to be named after the Major Arcana cards of a tarot deck.
 * Until Marceline's loss of her vampire self revived the vampires she absorbed, Marceline appeared to be the last vampire, having killed the rest. This became the case again once she re-vanquished them.