Marceline has light blue-gray skin, crooked fangs, and long, midnight black hair that reaches to her feet. She also sports two marks on her neck, which are the marks of the bite that turned her into a vampire. Her tongue is sometimes bifurcated, like a snake's, but other times looks like a normal human's. This may stem from her shapeshifting powers, allowing her to change its appearance.

Her main outfit features a dark gray tank top, dark blue pants, and red boots.

Secretly yandere and stalker