Marceline held a huge grudge against her father, Hunson Abadeer, because he ate her fries, as described in her "Fry Song". She also said that she didn't think he cared about or loved her due to the theft and his lack of acknowledgement of her feelings about it, which was more hurtful than the act of stealing her fries. This was made more explicit in Rebecca Sugar's original draft of the song, widely available on the Internet. When he steals her Ax bass, her grudge against him grew.
After Hunson learned how she really felt when Finn played him the aforementioned song as an attempt to stop Hunson's demonic rampage through Ooo, Hunson told her he loved her, and she reciprocated. They appear to have reconciled for the time being, but she still prefers that her father remains confined to the Nightosphere because it is too "emotionally exhausting" when he is around. Despite their undead natures, the two have a fairly classic teenage-daughter-to-father relationship, with underlying love but frequently heated disagreements on the surface, often about seemingly superficial things.
In "Daddy's Little Monster", Marceline asks Finn and Jake if they want to party in the Nightosphere. Finn is reluctant because he still thinks her father is evil, but she assures that he is "cool," perhaps meaning that they are on better terms. Later in the episode after Finn and Jake free Marceline from the Nightosphere amulet's control, she is shocked that her dad fooled her into wearing it; he had told her that it would grant her wishes, rather than forcing her to be the demonic ruler of the eponymous realm. Marceline's father confessed that he only wanted to be very proud of her, and Marceline told him that she wanted him to be proud of who she wants to be. He says he is proud of her, and smiles, so they may have worked out their issues.
In "I Remember You", in a flashback, a young Marceline is seen saying "Daddy? Daddy where are you?!" indicating that, for some reason, her father wasn't with her after the apocalypse. These details have yet to be explained.
In "Everything Stays", Marceline and her human mother are seen together in a brief pre-Mushroom War flashback. They appeared to have had a very strong bond with one another, and Marceline's mother is seen comforting a young Marceline, who is frightened of her weird dreams, with a song called "Everything Stays", which they sing together.
Marceline has a pet zombie poodle named Schwabl. Schwabl was seen briefly in her house in the episode "It Came from the Nightosphere" lying in the living room when Finn and Marceline were doing a song. It stood up and walked to another room once Finn started beat-boxing. Pendleton Ward has confirmed that Schwabl was based on his friend Marie's dog Schwabl. Schwabl was a white male poodle that had recently passed away, and is seen on the show as Marceline's dog that roams around her house. In "Marceline's Closet", there is a doggy door in the front that Jake uses to get into Marceline's house while Finn and Jake were playing Cloud Hunt. Schwabl is also a main character in almost all of Marceline's flashbacks as well as "Marcy's Super Secret Scrapbook" and the "Adventure Time: 2015 Spoooktacular".
Ice King/Simon Petrikov
Marceline and the Ice King were close friends during the aftermath of the Mushroom War when he was still Simon Petrikov, and he was the one who originally gave her Hambo. Marceline remembers her past connection with Simon, but the Ice King doesn't. Though Marceline discourages the Ice King from constantly coming to her house, she does not immediately force him out even when Finn and Jake arrive to take him away. Before the crown wiped his memory, he cared for Marceline and wrote her a note about their friendship while apologizing for leaving her and explaining why he had to, which she eventually reads. She finally admits to liking the Ice King, but only as a father-figure, as she stopped the Ice King from kissing her when he mistakes it for flirting and says she doesn't like him "that way." She is also visibly distraught when she realizes that he doesn't remember the meaning of the messages he left for her from before his transformation. She doesn't fully understand the consequences of the ice crown, and doesn't know how she can help or save him. They are seen together by Finn and Jake when they turn the messages into a song, as Marceline sheds tears while singing with her old friend.
In the Farmworld universe, Simon stops the Lich's existence by using his powers to stop the mushroom bomb from hitting Earth, but is killed in the process. Distraught by this act of bravery, Marceline protects his dead body for the next thousand years, even avoiding becoming a vampire just to protect him and, more importantly, his crown.
In "Simon & Marcy", she is shown to have deep feelings for the Ice King. She says she loves him, and invites him to play basketball with Finn and Jake. She is shown to have a strong emotional bond towards him, thinking of him as a father, and being worried about his well-being and sanity. She also reveals to Finn and Jake her history with him, meaning that she is not ashamed to have an affiliation with the Ice King.
In "Betty", Marceline faints when Simon informs her of his return. She sacrifices Hambo just so he can revisit his lost love for a short time to tell her he loves her.
In "The Empress Eyes", Marceline tries to protect the Ice King from The Empress, a Vampire who had hypnotized Simon and turned him into her thrall sometime before he completely succumbed to the ice crown. Marceline also reveals that Simon was the main reason she began hunting Vampires, and it is suggested that she fought The Empress in the past in order to free Simon from her control. She is forced to subdue the Ice King when he attacks her and Finn under The Empress' orders, and forces him to freeze The Empress. However, the Ice King shields The Empress, preventing Marceline from finishing her off. Despite previously following The Empress' orders and protecting her, the Ice King refuses to kill Marceline when The Empress commands him to. and it is revealed that the Ice King is actually immune to her hypnosis due to his mental state and was simply following The Empress' orders because of his infatuation with her. Marceline eventually kills The Empress with the help of Princess Bubblegum.
In "Take Her Back", while suffering from the effects of the scorpion envenomation she received from her battle with The Hierophant, Marceline has a dream where a slightly older version of herself visits Simon who is living happily with Betty.
Though they were initially enemies, Finn and Marceline soon befriend one another. Even when Marceline acts as a bully in her debut episode, "Evicted!", she is impressed by Finn's brave aggression and defiance and chooses to kiss him on the cheek after they fight. Both Marceline and Finn share the same spark for adventure and love of danger and excitement. Marceline is very good friends with Finn, who she seems to trust and is very comfortable being around.
One of the reasons Finn and Marceline befriend each other is that Finn saved Marceline's life in "Henchman" when Jake exposed her to the sunlight and threw garlic at her in a misguided attempt to help Finn. Although they were friends, Marceline still seemed to care about her Ax bass more than him, as seen in "It Came from the Nightosphere." In "Go With Me", Marceline makes it clear she does not want to date Finn, but Finn explains that he didn't want to date her either. They go to the movies together, but only as friends. More recently, Marceline has expressed that she does indeed care for Finn's well being. This is exemplified in "Heat Signature", where she becomes more protective of Finn when her ghost friends take pranking him and Jake too far on what started as a harmless "vampire initiation."
It is revealed in "Marceline's Closet" that Marceline still hides out in Finn and Jake's Tree Fort from time to time. In the same episode, Finn sees Marceline naked as she is about to take a shower, resulting in Finn being very flustered. Also, in the episode, Marceline forgives them for sneaking into her house even though she says not to.
In the episode "Daddy's Little Monster", Marceline's father states that he thinks that her friends, meaning Finn and Jake, are OK. After hearing this, she jests to Finn that she doesn't want to hang out with him anymore.
In "Bad Little Boy", Marceline tells a story centered on the interaction between her male-counterpart, Marshall Lee, and Finn's female-counterpart, Fionna. It is possible that she based the story on her own interaction with Finn. Even though Marceline claimed she only likes Finn as a friend, Marshall Lee seemed to think Fionna liked him more than that. It is also possible that Marceline wrote it as a love story only to please the other princesses, but the former statement could hint at Marceline's feelings for Finn.
"Simon & Marcy" marks the first time since "Daddy's Little Monster" that Marceline has hung out with Finn (not including "I Remember You"). She shows that they still have the same friendship they did in previous seasons, backing up that she was only jesting about not wanting to hang out anymore.
In the mini-series, "Islands", Marceline shows up to wish Finn and Jake goodbye, as they embark on a trip.
As an avid trickster, Marceline cannot resist scaring Jake whenever they meet. As he has a completely rational fear of vampires, Marceline often teases Jake and intentionally horrifies him when the chance is given. This perpetual bullying comes back to haunt Marceline, however, when Jake refuses to believe in her generally wholesome ways and nearly fatally wounds her in "Henchman."
In "It Came From the Nightosphere", Jake hides in Finn's pocket throughout the episode, implying that he is still afraid of her. Later in the season however, Jake gets over his fear, and he is often seen hanging out with Finn and Marceline as friends. He later considers himself a friend though, as evidenced in "Memory of a Memory". In the beginning of the episode, Rag Wizard informs Finn and Jake that Marceline is the one in trouble, and Jake begins to run faster. Later, when they run into the young Marceline and she asks who they are, Finn says "We're Finn and Jake!", and Jake says "We're your friends." Also, in "Go With Me", he called her "babe." It is of note, however, that Jake still holds some level of fear for Marceline, as seen in "Marceline's Closet", where he was noticeably scared of what she would do to him and Finn if she found out that they had broken into her house and hid in her closet.
In Season 5, they still seem to be friends. For example, in "Time Sandwich" when Jake had lost his sandwich to Magic Man, Marceline tells Jake, "Don't be sad." In "Red Starved" however, Marceline was deprived of anything red when they were trapped in a cave. She repeatedly mentioned, or tried, drinking Jake's blood, and later Jake tried to eat Marceline before she could eat him. At the end of the episode though, they appeared to be on good terms as they were before and have been since.
According to the original series pitch document, Marceline and Princess Bubblegum were intended to have a "friendly rivalry."
Princess Bubblegum shows discomfort around Marceline and appears to disapprove of her less-than-refined ways, while Marceline simply responds to this disapproval with mock affability, even teasing Bubblegum by calling her by her first name, "Bonnibel," and pointing out her supposed inability to show someone a good time. The two are shown to be able to clash easily, as seen in "What Was Missing", when Marceline sings "I'm Just Your Problem" to Princess Bubblegum, and spits on her jacket in the midst of a heated argument. In the same episode, it is revealed that Princess Bubblegum's stolen item is a t-shirt that Marceline gave to her some time ago. Bubblegum says that the shirt means a lot to her and she reveals that she sleeps in it. It is then revealed that Marceline herself had not even had an item stolen from her, but had been there solely for the company of those present.
Princess Bubblegum and Marceline's friendship is further explored in the comic Adventure Time: Marceline and the Scream Queens, in which Bubblegum becomes the manager of Marceline's band. However, the events expressed here may or may be not canon.In "Sky Witch", Princess Bubblegum is shown sleeping in the shirt from "What Was Missing", before waking and smelling it deeply. It is also shown that she has a picture of them in her closet, further indicating that she harbors sentimental feelings for Marceline. Later in the episode, Marceline flies into Princess Bubblegum's castle to ask her to help her find the eponymous sky witch, Maja. The Princess agrees to go with Marceline, who then flies her quickly out of the window and the Candy Kingdom. Bubblegum refers to Marceline as a "friend" when trying to get her to relax and pass through Maja's barriers. Although initially bemused when learning that Marceline has taken her to retrieve Hambo, the Princess softens as she realizes how important the teddy bear is to Marceline. Upon discovering that Maja is willing to fight to keep Hambo, Bubblegum barters for Marceline's most beloved treasure by offering her most beloved treasure: the shirt Marceline gave her, which is stated by Maja the Sky Witch to have more "sentimental freshness" and "psychic resonance" than Hambo. Bubblegum gives Marceline Hambo and the two are shown flying away, Bubblegum clinging to her back.
It was revealed in "Time Sandwich" that the two were on good terms with each other, as the two did not argue or show any discomfort around each other.
In "Red Starved", Marceline bites Bubblegum and drains her in her hunger, concluding that what she had sang in "I'm Just Your Problem" is true. This did not break the two up, as shown in "Princess Day", where both were texting each other on their phones. Marceline had invited Bubblegum to ditch the event, but the invitation is rejected as she wants to finish a crossword puzzle.
In the episode "Varmints", Marceline is trying to find Princess Bubblegum so they can go to the Squeez-E-Mart together. She is surprised to find that the King of Ooo is in Bubblegum's bed and that Bubblegum has been exiled from the Candy Kingdom. When she finds Bubblegum, Marceline is upset that she was uninformed about the exile. This suggests that Marceline cares deeply about Bubblegum and expects to be kept up-to-date on Bubblegum's life.
Later in the episode, Marceline and Bubblegum chase some varmints down into the Rock Candy Mines. Marceline states that she and Bubblegum often hung out down in the mines, before Bonnie got too busy being the Princess of the Candy Kingdom. They eventually come upon a graffiti tag Marceline made Bubblegum write when they used to hang out in the mines.
When they are back in the Princess' cabin, Bubblegum confides that she has been "crazy tired" for a long time, but Bubblegum still insists that she must watch for more varmints. Marceline tells PB to worry about the varmints tomorrow, and that she will look out for them throughout the night. Bubblegum agrees to rest, but only if Marceline promises to wake her up in fifteen minutes. Marceline promises. The episode ends with Bubblegum resting her head on Marceline's shoulder. This episode shows that Marceline and Princess Bubblegum have a long and complex relationship. The end of the episode shows that their relationship has become very trusting and caring, as Bubblegum trust Marceline to wake her.
In "Take Her Back", Marceline is shown to be having a dream in which she is living in Princess Bubblegum's cabin with her. Marceline has grown very old and Peppermint Butler is outside digging Marceline's grave. Bubblegum has not aged, but has only grown taller. Marceline's dream seems to be caused by Marceline's anxieties about being mortal. Her dream suggests that she does not want to grow old because Princess Bubblegum will not be aging with her.
Towards the end of the episode Princess Bubblegum invites Marceline to live in her castle. Marceline turns down the invitation.
In "Seventeen", Marceline and Bubblegum are shown holding hands as they approach Finn after he was defeated by Fern. This short scene was highlighted by Cartoon Network in an Instagram post on December 7th, 2017 which advertised the release of "Seventeen," "Ring of Fire," "Marcy & Hunson" and "The First Investigation" on the Cartoon Network app.
In "Marcy & Hunson", Hunson Abadeer asks Finn, "So what's my little monster up to these days? Is she still all goody-goody? Still half vampire? Started dating anyone?". Finn replies, "Yes. Yes, but no, then yes again. And maybe?". Finn's response to Hudson suggests that Marceline may be romantically involved with someone. Perhaps Finn's confusion is a result of seeing Marceline and Princess Bubblegum holding hands in "Seventeen". Later in the episode, Marceline sings the song "Slow Dance With You". The lyrics, "I know all the other boys are tough and smooth, and I've got the blues. I wanna slow dance with you," can be interpreted as Marceline longing to dance with someone who has many male suitors such as Princess Bubblegum. The song could also be interpreted to be a cover of a song written by someone else, thus when Marceline says "I" she is not actually referring to herself.On August 7th, 2014, at a Barnes & Noble book signing for Martin Olson's book, The Adventure Time Encyclopædia, Olivia Olson confirmed that Marceline and Princess Bubblegum had dated; which can explain their rivalry and why they had trouble getting along with the other in the past. Since the show airs in some countries where same-sex relationships are illegal, Marceline and Princess Bubblegum's relationship cannot be depicted on the TV series. Olivia stated that their relationship may be mentioned in the upcoming book, but had no further statements regarding the two. However, a since-deleted tweet by Olson following the panel suggests that she may have been joking. The no-longer existing tweet had stated, "I like to make things up at panels. Ya'll [sic] take my stories way too seriously..." suggesting she made up the story. The tweet was removed shortly after being posted for reasons unknown.
On August 20, 2014, Rebecca Sugar hosted an "Ask me Anything" on Reddit. When asked by a fan "any comments about Marceline and Bubblegum's, [sic] and their shared history?" to which she replied, "doesn't seem that recent to me!" suggesting that fans had been right about their backstory since long before the supposed confirmation of their relationship as friends, not as former lovers.
In August 2014, Hynden Walch, voice actor of Princess Bubblegum, confirmed on Tumblr that they used to be best friends. However, Princess Bubblegum "matured" (meaning that Bubblegum was being too much of a princess which made her distant with Marceline) too fast for Marceline's liking, splitting apart their friendship.This explains their rivalry, along with why Princess Bubblegum has trusting issues, and also why Marceline knows PB's first name, Bonnibel.
See Princess Bubblegum's relationships for more information.
It seems that Marceline and BMO have a friendly relationship; she is seen playing BMO during the "House Hunting Song" in "Evicted!" and comments on how she thinks it's cute. Later, in the episode "What Was Missing", Marceline calls BMO "baby" while helping it install an electrical lead to cook her and her other friends some noodles.
In the comics, although these presumably reflect a separate canon, BMO is shown to be happy when Marceline visits Finn and Jake at the treehouse.
Lumpy Space Princess
Marceline teamed up with Lumpy Space Princess to prank Breakfast Princess in "Princess Day". Marceline decided to help her after witnessing an argument with Breakfast Princess. This impressed Marceline because she liked LSP's vibe, while LSP reciprocated because she thought that Marceline is "bad". During the episode, the girls hi-five several times and remained good friends.
In "Be Sweet", Lumpy Space Princess calls Marceline to brag about her babysitting job, showing that the two remained friends after "Princess Day". In "The Music Hole", Lumpy Space Princess plays drums for Marceline in the Battle of the Bands.
Duke of Nuts
Marceline appears to be friends with the Duke of Nuts, although their history has not been revealed.
Ash is Marceline's ex-boyfriend. They lived in Finn and Jake's Tree Fort together prior to them moving in. Ash performed spells to impress Marceline and called her "Mar-Mar." Eventually Ash sold Hambo, Marceline's beloved childhood toy, resulting in her becoming enraged and dumping him. They seem to share a punk-like style.
In "Memory of a Memory", Ash poses as the Rag Wizard and pretends Marceline is under a sleep spell in order to trick Finn and Jake into removing the memory of their breakup. She then falls back in love with him, but once Finn explains the situation to Marceline, she becomes enraged again and kicks Ash in the groin, followed by a heavy pummeling by her and Finn, and later Jake. He seems to have no respect for her, as he only wants to date her so she can make him dinner and do other chores.
After parting ways with Simon Petrikov and living on her own, the half-human/half-demon Marceline began hunting Vampires to protect the human population that survived the Mushroom War. In "Everything Stays", it is revealed that during her Vampire hunting career, she discovered she could gain their powers by absorbing dust produced after a Vampire dies with the soul sucking ability she learned from her father. According to Princess Bubblegum, Marceline has killed tons of vampires during her career as a Vampire Hunter and was responsible for the near extinction of the vampire race, however ended up being turned into a vampire as result of her battle with the last surviving vampire. Despite having lived as a vampire herself, Marceline shows contempt for blood sucking vampires she has battled in the past.
The Fool is one of the first Vampires Marceline ever targeted, and while she hunted him with deadly earnest, he regarded the whole thing as a game of tag. Marceline managed to defeat him and used her soul sucking power to gain his power of flight and levitation. After he is revived, The Fool is the first Vampire Marceline stakes and kills in "Vamps About" allowing her to regain his power of flight. Marceline dispatches with him with absolutely no effort, while The Fool casually shrugs off being stabbed in his usual carefree fashion.
Marceline has a deep hatred toward The Empress which is implied to be due to her hypnotizing Simon Petrikov and turning him into her thrall sometime prior to his full transformation into the Ice King, toying with him and forcing him to preform degrading such as licking her boots. To protect Simon, Marceline fought and killed The Empress, absorbing her power of invisibility before her battle with The Hierophant. After The Empress is revived and Marceline learns she is targeting the Ice King again, Marceline races to the Ice Kingdom to stop her from harming or manipulating the Ice King. After managing to subdue the Ice King, Marceline forces him to freeze The Empress. However, Ice King tries to stop Marceline from killing her, and The Empress orders the Ice King to kill Marceline, but he refuses. When The Empress tries to place him under deep hypnosis it is revealed that the Ice King is immune to The Empress's hypnotic powers and was simply infatuated with her in typical the Ice King fashion. With help from Princess Bubblegum, Marceline manages to kill her and reclaim her power of invisibility.
The Hierophant initially avoided fighting Marceline during the Vampires' attack on the ship carrying Two Bread Tom and the surviving humans by disguising himself as Marceline's pet zombie poodle, Schwabl. His deception was uncovered however, when Two Bread Tom noticed that Schwabl was wearing boots. Marceline fought The Hierophant in order to protect the remaining humans and their ship. She managed to kill him and claimed his shapeshifting powers. After his revival, The Hierophant parts ways with the other revived Vampires and tries to ally himself with Marceline, but she refuses. During their fight, Marceline is poisoned by The Hierophant's scorpion tail, and becomes incapacitated due to not possessing The Moon's regeneration and self-healing powers, forcing her friends to deal with The Hierophant. Fortunately, Jake learns from Peppermint Butler that The Hierophant is an old school vampire and cannot enter a house unless he is invited. Jake shapeshifts into a house which Finn, PB, and Marceline take shelter in. The Hierophant is eventually killed when Crunchy knocks through the doorway of Jake's house form, because he was not invited in. Marceline manages to reabsorb his power to shapeshift, however she collapses from the Hierophant's scorpion venom.
Marceline had killed The Moon and obtained her self-healing powers before her initial battle with The Hierophant, which allowed Marceline to survive being cut in half during the battle. In "May I Come In?", Marceline hunts The Moon, along with Finn, Jake, and Princess Bubblegum, after she and the other Vampires were revived by, following her trail of moon pearls, but they end up running into The Hierophant instead. Marceline claims that fighting The Moon is like "fighting a cutting board" due to her self-regeneration powers. In "Take Her Back", Marceline is unable to resume hunting her due to having been poisoned by The Hierophant in "May I Come In?", forcing Finn and Jake to hunt The Moon down while Princess Bubblegum tries to find an antidote to poison. The Moon proves to be too much for Finn and Jake to handle, and manages to corner PB and Marceline. Fortunately, Peppermint Butler manages to kill The Moon by thrusting a giant stake through her back and into her heart, allowing Marceline to reabsorb her healing powers and cure herself of The Hierophant's poison.
The Vampire King is Marceline's arch nemesis and was the last Vampire to be killed by Marceline. Marceline had fought him in an epic battle that resulted in his defeat and death, however before turning to dust, the Vampire King managed to bite Marceline, and thus is the vampire responsible for turning her into a vampire herself. In "Everything Stays", Marceline accidentally causes the Vampire King and the other Vampires she had absorbed to be revived when she had Princess Bubblegum cure her of her Vampirism. Upon learning of this and the other Vampires' revivals, Marceline became determined to hunt him down and refused to accept his claims that he had changed. After killing the other Vampires and regaining their abilities, Marceline confronted the Vampire King. The Vampire King revealed, however, that he had grown tired of being a vampire, and asked to be cured of his Vampirism like Marceline. She eventually agrees and has Princess Bubblegum use her machine to remove the Vampire King's pure vampire essence, causing him to revert back into a normal Lion. However, his pure vampire essence is accidentally unleashed, resulting in the creation of a Dark Cloud Monster. Marceline ends up losing her will to fight, forcing her friends to fight Vampire Cloud on their own. The Ice King helps her regain her resolve, and she races to aid her friends in defeating the Vampire Cloud. Marceline uses her soul sucking powers to absorb the Vampire Cloud, however like her past battle with the Vampire King, she bitten in the process, turning her back into a vampire, though she states she is now fine with it. She discovers that as a result of absorbing the Vampire King's pure vampire essence, she can now see and communicate with a miniature mental projection of the Vampire King.