Demonic Genes: From her demonic father, Marceline has the ability to absorb people's souls. In addition, Marceline has enhanced speed, strength, and senses (mostly sight, hearing, and smell). Marceline, had she not been turned into a vampire, her natural lifespan still would've been extended. Marsha also possesses the ability to possess bodies via entering a body through black smoke and the ability to make deals where she does something in exchange for something (a deal that can be magically enforced). She also has a high resistance to fire. In addition, Marceline has some magic capabilities such as being able to cast a red beam that restrains people, minor control over fire, and the ability to raise the dead.
Vampirism: After absorbing the essence of several powerful vampires, Marceline gained several supernatural powers. From The Fool she gained the power to fly; from The Empress the ability to turn invisible; from The Hierophant she gained the power to shape-shift; and from The Moon, the ability to rapidly heal. As a vampire, Marceline is immortal, youthful, and unaging as a vampire and as long as she's not contacted by any form of typical weakness that can kill vampires, she could live both forever and eternity.
Vampire Cloud Form: As a result of absorbing the Vampire King's dark cloud half, she can now communicate with a miniature mental projection of him. During the turmoil of the Gum War, Marceline was able to release the vampiric essence she absorbed from the Vampire King, transforming into a similar black, cloud-like form. In this state she was powerful enough to defeat one of the creatures created by GOLB.
Musical Talent: Marceline is a very talented musician and songwriter, and is proficient at singing and playing her basses.
Vampire Weaknesses: Due to being a vampire, Marceline is vulnerable to typical vampire weaknesses. She burns in direct sunlight, although it should be noted that she does not dissolve right away and can move around in sunlight if she covers herself sufficiently. In addition, Marceline can't see herself in normal mirrors.
Feral State: Whenever she doesn't consume enough red-colored objects, Marceline goes into "feral mode", a state in which she becomes ravenous out of hunger. This rabid state subsides once Marceline consumes a sufficient amount of red.