Marceline lives on her own in a small house in Ooo. She doesn't see her dad often because 'he ate her fries' and because he spends a majority of her time stealing people's souls, which Marceline finds irritating. In the episode It Came From the Nightosphere, Finn summoned Marceline's father by accident, which she found annoying because he tried to steal all the souls in Ooo (when he is in his Monster Form you can see all the souls he has eaten, even though he had also eaten Lumpy Space Princess, who claimed to be there because she was 'crashing a party'). It is unkown who Marceline's mother is or if Marceline has any siblings. She was called 'Marcie' by Simon, the regular Ice King until he went crazy.
Marceline, like most vampires, has fangs and pale skin. She is exceptionally tall and has long black hair. She usually wears casual, but somewhat goth-like clothes, like jeans and a black shirt. Her eyes are just black dots.
Like many vampires, Marceline has super strength and speed, though these are not portrated often. Marceline sings and plays bass. (She turned her father's axe into a bass.) She is also skilled at trickery, as shown when she tricks Finn and Jake into thinking they're vampires. Marceline can float and has basic vampire powers. However rather than eat blood, she eats 'shades of red' because she claims they taste better.