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 fact it was her fries that he stole. 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. However, 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 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 her of what she is. 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.
SchwableEditMarceline has a pet zombie poodle named Schwable. Schwable 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 walked up and went to another room once Finn started beat-boxing. Pendleton Ward has confirmed that Schwable was based on his friend Marie's dog Schwable. Schwable is a white male poodle that has 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.
Ice King/Simon PetrikovEdit
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 of her house even when Finn and Jake arrive to take him away. Before the crown wiped his memory, he cared for Marceline for a time and wrote her a note about their friendship while apologizing for leaving her and explaining why he has to, which she eventually gets to read. She finally admits to liking the Ice King, but as an old grandfather-figure of some sort, since she stopped the Ice King from kissing her when he mistakes it for flirting and saying she doesn't like him "that way." She is also visibly distraught when she sees that he doesn't remember the meaning of the messages he left for her before his transformation into the Ice King because she does not know the consequences involved in Ice King's crown, and as she doesn't know how she can help him. She is last seen with him when they turn the notes into a song, and she is shedding 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, the ice 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.
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 and seems to trust him and be very comfortable with him.
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. However, though they are now friends, Marceline still seems 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. 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 prank him and Jake too far on what started to be a harmless "vampire initiation."
It is revealed in "Marceline's Closet" that Marceline sometimes still hides out in Finn and Jake's Tree Fort. 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 she finds this out 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's female-counterpart, Fionna. It is possible that she based the story on her own interaction with Finn. However, even though Marceline claimed she only likes Finn as a friend, Marshall Lee seemed to think Fionna liked him more than just as a friend. To be fair though, she wrote it with the intention of a love story to please the other princesses.
"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.
As an avid trickster, Marceline cannot resist scaring Jake when their two paths meet. Seeing his 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 almost fatally wounds her in "Henchman."
In "It Came From the Nightosphere," Jake hides in Finn's pocket when he is with Marceline, implying that he is still afraid of her. However, later in the season, Jake gets over his fear, and he is often seen hanging out with Finn and Marceline as friends. He might even be fully considered a friend as evidenced in the beginning of "Memory of a Memory," when after the Rag Wizard (Ash in disguise) informs Finn and Jake that Marceline is the one in trouble, he begins running faster, and later in the episode, when they run into the young Marceline and she asks who they are, Finn says "We're Finn and Jake!" then Jake says "We're your friends." Also, in "Go With Me," he called her "babe." It is still notable, however, that Jake still holds some level of fear for Marceline, as seen on "Marceline's Closet," where he was noticeably scared of what she would do to them upon the realization that he and Finn broke into her house and hid in her closet.
In season 5, Jake is seen playing with Marceline along with Finn and Ice King, implying that they are still friends. However in "Red Starved" it was shown he held great fear of Marceline, especially when she is angry at him.
It seems that Marceline and BMO have a friendly relationship: she is seen playing it 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.
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. 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 there.
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 Marceline, 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 of some sort for Marceline. Later on in the episode, Marceline enters the castle: flying past a Gumball Guardian, pushing it out of the way, entering the window to where the princess is standing, and closing the curtains, all without the Guardian complaining. Marceline asks Princess Bubblegum 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 "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 later revealed in the episode "Stakes of Gum" that Princess Bubblegum and Marceline do have feelings for each other. Bonnibel came to watch Marceline's concert because she loves her music, Marceline invited her backstage. When Marceline sung an extended version of I'm Just Your Problem and Oh, Bubblegum, Bonnibel realised that Marceline also had feelings for her and they started a secret relationship.
In "Couple Night" they finally revealed their relationship to the others after the whole couple night had become a disaster. In "Garlic and Peanut Butter" Marceline took the step to introduce Bonnibel to her father. At first Hunson didn't approve of the relationship which caused trouble for both girls. Hunson eventually approved and they could be open about their relation. Their love for each other was shown again in "Sweet Revenge" in which Princess Bubblegum gets kidnapped by Dark Princess, but luckily gets saved by Marceline. PB in favor tries to find a way to make the Unknown Lands a dungeon.
The relationship between Marceline and Gene is very complicated. It was revealed in "Only Three Wishes" that Gene and Marceline had met each other in their teen years, when Marceline was residing in the Nightosphere with her dad and had not yet moved out. Marceline owned Gene because she found his lava lamp but knew he would be gone if her third wish was granted, but wanted to wish for his freedom.
They grew very close to each other, but never got into a confirmed relationship. When Marceline wished for Gene's freedom the Grand Master Wizard appeared and took Gene away to stand trial. Marceline was saddened and got into a relationship with Ash afterwards, explaining why she became so commited to her new relationship. Ignoring the fact that he was a douche.
Marceline and Gene met again later but didn't want to continue the relationship, as it would be too awkward. They however became 'friends with benefits'. Till the day of today they often hang out, but don't talk about their relationship to anyone. She doesn't love him, as she loves Princess Bubblegum, but different, as they still have their 'little adventures'. Which is something only PB is aware of. This may also conclude the fact that Marceline is probably bisexual.
Dark Princess is the nemesis of Marceline. She first meets her in "Trapped in the Dark" in which she is captured by Dark Princess and kept prisoner. It was quickly revealed that Dark Princess held a grudge for Marceline's father, Hunson Abadeer, because he killed her father. And now she wants to take revenge on him by killing Marceline.
The reason why Hunson Abadeer killed her father was because he discovered that he was the one who killed Marceline's mother, who was on Earth to protect Marceline. Hunson discovered that after Simon Petrikov brought Marcy back to the Nightosphere instead of her mother. He kept this from Marceline because she didn't want to hurt her. However other than the reason that Hunson called Dark Princess' father she has no motives to like or dislike Marceline.
Ash is Marceline's ex-boyfriend. They lived in Finn and Jake's Tree Fort together before they moved 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 the breakup. She then falls back in love with him, but once Finn shows and explains the situation, she becomes enraged again and kicks Ash in the groin, followed by a heavy pummeling by her and Finn, and later Jake. He does not respect her at all, as he only wants to use her to make him dinner and do other chores.