Marceline is a 1000 year old Vampire, so it is possible that she lived in the time The Great Mushroom War happened. In the episode "Memory of A Memory," parts of her past was revealed that she used to have a doll named Hambo. Like when it showed her much younger self in a ruined city. She mention that she was playing with a hoola-hoop in the Fire Kingdom in "Evicted!" She does have parents as she stated in "Henchmen" that her mother used to patch her up when she was a little kid. Her father appeared in the episode "It Came from the Nightosphere," and him and Marceline have a bad past but Marceline's father seems to be calm when around her. In the episode "What Was Missing," Princess Bubblegum and Marceline seem to have some sort of feud. It is unknown how long they have hated each other. Marceline used to have a boyfriend named Ash who took her favorite bear (Hambo) and sold it to a witch, for a new Cherry Blossom Wand, which is when Marceline dumped him, and moved out of the house. Marceline and Ash used to live in the Tree Fort, but then moved into the cave for an unknown reason. then got back together It is shown in the episode "I Remember You" that Marceline and Simon Petrikov were once friends, after The Great Mushroom War had happened and her father was in the Nightosphere.
She's a sexy vampire lady. ^.^
Her past is mostly about Ash and Hambo.
There was a Vampire King but she killed him according to Ward.
No, the king is her dad, she says that she's the vampire queen but she's the vampire princess.
Hudson Abadeer is the king of nightosphere, not the vampire king.
Her mother could be the vampire queen, so she is the vampire princess.