Marceline’s mom, Elise, passed away due to a terminal illness after the Mushroom War.
Marceline the Vampire Queen is a central character in the animated television series “Adventure Time.” Her mother, Elise, is introduced in the series through flashbacks and additional lore. Elise’s story is particularly expanded in the “Adventure Time: Stakes” miniseries and the episode “Everything Stays,” where it is revealed that she survived the Mushroom War along with young Marceline.
After the war, Elise and Marceline lived in a post-apocalyptic world, and during this time, Elise was shown to be suffering from a cough, which was later revealed to be a symptom of a terminal illness. Despite her condition, Elise tried to provide a sense of normalcy and care for Marceline, teaching her songs and comforting her. Unfortunately, as her illness progressed, Elise realized she would not be able to care for Marceline much longer.
In a poignant moment, Elise recorded a message for Marceline on a cassette tape, expressing her love and giving her daughter advice for the future. She then left Marceline in a makeshift shelter, presumably to protect her from witnessing her final moments. It is implied that Elise succumbed to her illness shortly after, leaving Marceline to fend for herself in the dangerous world. Marceline’s memories of her mother and the trauma of losing her played a significant role in shaping her character throughout the series.