Marceline's Mom

 was briefly mentioned by Marceline in "Henchman" while Finn and Marceline were in the strawberry fields. Marceline claims that when the sun burned her, it reminds her of when she would scrape her knees and her mom would patch her up. This is the only thing that has really been said about Marceline's mother currently.

In "Return to the Nightosphere," one of the background images shows Marceline as a child, Marceline's father, and an unknown female figure with long black hair similar to Marceline's. It could be speculated that this picture is an Abadeer family photo and the unknown female is Marceline's mother.

In "Memory of a Memory," a picture is shown to the left of Marceline's couch in her living room, both in the real world as Finn and Jake are falling asleep, and in the dream world. The picture is of a woman with long, black hair and blue skin holding a baby with blue skin. This was confirmed to be a picture of Mary and baby Jesus, though.

Farmworld Marceline stated that she is half demon, therefore her mother was something other than a demon.