Marceline's Mom

Marceline's mom was a human woman who was alive around a thousand years prior to the current setting of Adventure Time, and who had a daughter with Hunson Abadeer, Marceline. She was first mentioned in "Henchman" while Finn and Marceline were in the strawberry fields, where Marceline states that when the sun burns her, it reminds her of when she would scrape her knees as a child and her mom would patch her up.

Marceline's mother makes her first physical appearance in "Everything Stays" in one of Marceline's flashbacks, where she is shown living with her daughter in what seems to be a trailer. She is briefly seen telling Marceline about how she met Hunson. When Marceline says that she does not want to take a nap because her dreams are weird, Marceline's mother comforts her by telling her that her dreams might just be normal things viewed from a different angle and singing her a lullaby, "Everything Stays".

Considering the time frame of her appearance, she likely perished with the vast majority of mankind in the aftermath of the Mushroom War, or if she survived, died from old age.

Background
In "Finn the Human", Farmworld Marceline states that she is half-demon, which is the first indication that Marceline's mother was of a non-demon species.

Marceline's father makes a brief, mournful reference to Marceline's mother in the The Adventure Time Encyclopædia: "Thus, regarding her childhood adventures with her poor, unfortunate mother, there is, now and evermore, naught to be heard but the Shadowfall of Nightospheric Silence."

Marceline's mother is heavily mentioned in Adventure Time: The Enchiridion & Marcy's Super Secret Scrapbook. Being so young, Marceline only had a few scarce memories of her mother, who mysteriously vanished by the time Simon Petrikov found her. All that she left behind were two photos of her and Marceline together and a letter placed in Marceline's pocket mentioning Hunson and to keep Marceline safe. Before hibernating, Marceline looked up the last two pictures of her mother to cherish their memories together and hoping that she would dream about her.

Trivia

 * She was first confirmed to be a human at Wondercon 2013.
 * Her voice actress, Rebecca Sugar, formerly worked on Adventure Time as a writer and storyboard artist before creating her own show, Steven Universe, which also airs in the US on Cartoon Network.
 * As of the episode "The Dark Cloud", whatever happened to her currently remains unknown.

Madre de Marceline