Marceline grew up around the era of The Great Mushroom War, and she and her father survived because of their magic powers, but her mother most likely died in the war because she was a human.
In a memory which takes place prior to the Mushroom War, young Marceline and her mother are seen living normally in a trailer home. The succeeding flashbacks all take place in the aftermath of the war. In a destroyed city, Simon records a VHS message for Marceline before parting ways with her.
Remaining inside while the others escape, Betty uses the Ice King's crown in its wish-granting state to protect Simon and sacrifices herself, making her and GOLB fuse into one being.
She is ethnically Black on her mother's side, but her skin is bone-white because of her father, a demon with pale blue skin. Having spent centuries traversing the Land of Ooo, she has evolved into a "fearless daredevil", and her fondness for mischief has turned her into something of a trickster.
The Untold Story of the Great Mushroom War (Adventure Time)
Why does Marceline eat red?
Unlike traditional Western vampires, Marceline subsists not off blood, but rather the color red (including "low-grade" shades such as pink). Since she is only sated by the color itself, blood is appealing simply due to its hue (although Ward noted on his Formspring that she "drinks blood sometimes").
Simon's fiancée Betty Grof (Lena Dunham) left him as a result of the crown's influence over him. The crown's magic allowed him to survive the apocalyptic Mushroom War.
Though a good person, Betty would temporarily become evil once she gained the powers of Magic Man after arriving, through time travel, to the Land of Ooo.
As a last-ditch attempt to stop the war, Jake unleashed the nightmare juice given to him and Finn by Nightmare Princess, forcing him, Finn, PB, Gumbald, and Fern into a hallucinatory slumber.
Finn was, for a long time, the only confirmed human in the Land of Ooo, to the point where he had an epithet, "The Human", and was referred to by many as "Finn the Human". The reason for this is revealed in the episode "Her Parents," as Lady Rainicorn's dad believed that humans were extinct.
In "Gold Stars", it is revealed that the Lich's power and evil is still contained within Sweet P, and can take over when Sweet P is threatened and emotionally charged.
Another item able to work against The Lich is the sweater Princess Bubblegum gave to Finn. Imbued with the power of "liking someone a lot," the sweater protected Finn from The Lich's flames, and was later used as a weapon. With it, Finn was able to attack The Lich and reduce his body to dust.
Shermy is confirmed to be a reincarnation of Finn, which makes sense considering their similarities and the fact that Finn can resurrect when he wants and be another living being due to being an incarnation of the Blue Catalyst Comet.
In another memory Marceline is seen to have grown up and appears a teenager and still doesn't have any bite marks, proving further that then she wasn't a vampire because vampires don't age. Since her father is an immortal demon but her mother was a human, she probably aged very slowly.
Closer analysis of the Black Hood's eyes and Betty's dad's eyes proves a significant similarity between the two, with Svenson's eyes just not quite there. Fans are also speculating the Black Hood might be Betty's brother who is yet to make an appearance on the show, hence his obsession and personal interest in Betty.
Betty and Veronica are best friends, though this wasn't always the case. At first, Veronica kissed Archie during Cheryl's after-party, thus bringing an end to the brief friendship as it quickly turned to somewhat of a rivalry over the affections of Archie Andrews.
It's later revealed that Hal had been in cahoots with the Red Dahlia, Penelope Blossom and the Gargoyle King, Chic. After Hal failed to stop Betty and her friends, he was shot in the head and killed by Penelope.
Moseph "Moe" Mastro Giovanni was an old man who founded MO Co. and created BMO and all the other MOs. He says that BMO was created to experience fun and to care for his son, but he never managed to start a family. When asked by Finn if he was a human, he responded that his skin is human.
His crown has made him insane over the years, affecting his social skills, causing him to unintentionally do bad things. Friendship and companionship is all he really wants, though he goes about it the wrong way. Due to the insanity brought by wearing the crown, Ice King seems to have limited memory.
His current biological age is 34, as stated by Steve Wolfhard in the Conversation Parade podcast, meaning that at some point his aging slowed down from when he was a puppy. Jake says in "Daddy-Daughter Card Wars" that he's lost track of how old he is, but thinks he might be almost 40.
Marceline and Bonnibel kiss romantically, rekindling their love for each other. Marcy and Bonnie together at last. But finally in the series finale, "Come Along With Me ", Marceline sees Bonnibel get crushed by an enemy. Enraged, she attacks it and manages to hold it off.
In the Episode Graybles 1000+ Cuber is stranded on Ooo but 1000 years in the future from what we can tell from the episode, almost all life is gone, Marceline is probably still alive, IK has evolved into a demonic ice creature, Finn and Jake's tree house has grown into the sky.
Princess Bubblegum (Real Name: Princess Bonnibel Victoria Bubblegum) is a main character of Adventure Time. She made her first appearance in the animated short "Adventure Time!." She is the ruler of the Candy Kingdom.
