Finn the Human

Finn is the main protagonist of the series Adventure Time. He fights for the great or good, and he's the only human in his world. He joins Sora's team for the best adventure he's ever had.

In Adventure Time

As shown in "Memories of Boom Boom Mountain," Finn appears to have been abandoned in the woods during infancy. He reveals that he made "boom boom" (Finn's word for defecation) on a large leaf, fell on it, and lay there crying until Joshua and Margaret (Jake's parents) rescued him from the wilderness to raise him alongside Jake, who becomes like a brother to him (as such, Jermaine is also Finn's adoptive brother). In "Memory of a Memory," a baby Finn is seen singing a song in the bathroom of what appears to be Joshua and Margaret's house. In "Henchman," when Finn is asked about his parents, he says Jake told him that he came from a cabbage, in jest. In "Susan Strong," Finn states that he knows nothing of his human parents or any other humans.

Status as the last human

Finn is the only confirmed human in the Land of Ooo. In the episode "Her Parents," Lady Rainicorn's dad says he thought humans were extinct. This lends new significance to his title "Finn the Human," as his humanity may be unique in Ooo.

Up until "Susan Strong," Finn believes he has never met another human. Finn becomes morose and "soul-searchy" when he thinks about it. In the same episode, Finn encounters Susan Strong. Even though the other members of Susan's tribe of Hyoomans were revealed to be mutants, Susan's identity as a human or mutant is left ambiguous. In "Beautopia," it may be true that Susan is also a human, but it was not confirmed. The businessmen are also likely humans, but their minds have been damaged by being frozen for so long, and they talk like zombies. They also have boils all over their face, which may also be a result of being frozen.

Other "human" characters (such as Penny, Phil or the Old Man Henchman) have been confirmed by the show's creator, Pendleton Ward, to be mutants or humanoids. According to Pendelton Ward's FAQ page, even Finn is mutated in some way.

Fionna is also a human, although she is just a character in Ice King's fan fiction. Ice King was formerly a human, as shown in "Holly Jolly Secrets Part II."

Personality

Though at times violent and aggressive, Finn is a brave and righteous hero. He has a very strong sense of responsibility and gets upset when he is unable to help others. He seems to be somewhat overprotective of his friends; such as when Tree Trunks almost got killed in the episode "Tree Trunks" and Jake in "The New Frontier." He is almost physically incapable of doing anything evil or unjust, and will struggle greatly against doing such things, as seen in several episodes such as "City of Thieves," "Mortal Recoil," "The Eyes," and "The Enchiridion!" Even though he acts like a normal boy, Finn acts like a gentleman when it comes to ladies. As revealed in "Davey," despite his heroic nature, he also takes a liking to a "normal life" without any recognition or praise for being a hero.

Finn is shown to be a fearless thrill-seeker and enjoys putting himself in the midst of danger simply because he enjoys a challenge. However, as illustrated in "Ocean of Fear," Finn has an unexplained phobia of the ocean, or thalassophobia, despite the fact that he can effortlessly come into contact with any other body of water. While he portrays himself as a rough and tough hero, Finn has a tender side capable of love and compassion, as shown by his boyhood crush on Princess Bubblegum and his brotherly relationship with Jake. However, Finn seems to hate romance movies and kissing because in "Go With Me," he actually vomits during a kissing scene in a movie. However, at the end of "Dream of Love," Finn was not grossed out by Tree Trunks and the Pig kissing. Finn's growth in accepting romance and physical love is also demonstrated when he willingly kisses Princess Bubblegum in "Too Young" and his current girlfriend, Flame Princess, in "Burning Low."

Finn’s aspirations to be a great hero makes him somewhat of a moral sheriff in the Land of Ooo, as he is willing to help and protect any innocent person or creature. Finn appears to be somewhat simple-minded, seeing that he gets a lot of conflicting emotions when it's unclear whether something is good or evil (exemplified by his dealings with Marceline in the episode "Henchman").

Many aspects of Finn's personality are shrouded in mystery. In the episode "Rainy Day Daydream," it was shown that Finn believes "imagination is for turbonerds who can't handle how kick butt reality is," showing Finn not only accuses imagination users as "turbonerds" and believes life is fantastic. Finn then refused to use his imagination until he had to reactivate Jake's "bombastic personality" in his imagination land, (which was just a basic gray and white empty plane hinting that Finn isn't very imaginative, but that was contradicted in "Power Animal" when the gnomes harnessed the energy from Finn's imagination) which was inhabited with a few dainty creatures such as Bellamy Bug. Finn's imagination was than powerful enough to effect the real world (like Jake's but to a lower degree) and turn on Jake's imagination.

Finn can also be very stubborn; such as in "Memories of Boom Boom Mountain," "Wizard," "Dungeon" "Rainy Day Daydream," and especially in "Another Way." Finn can also be easily tricked, as in "The Eyes" when Jake convinced him that the giant hawks would take the horse to a land of sunshine and love stuff and take care of him. He can get overly angry and yell as in "Trouble in Lumpy Space" and "Tree Trunks," but he immediately feels guilt and remorse and apologizes when he can. Finn prefers to do work and not take the easy way out ("Business Time") and ("The Real You").

While Finn is shown to be a courageous warrior, he is also shown to have several fears. In "Another Way" and "King Worm, he is shown to have a fear of clowns. Also in "King Worm" he is shown to have a fear of Bubblegum calling him too young, and he also fears the return of the Lich, or possibly just the Lich himself. He is also shown to fear the Ghost Lady ("King Worm," and "The Creeps") and the ocean ("King Worm," and "Ocean of Fear").

Abilities

Physical

Finn is proficient in several forms of combat, including hand-to-hand combat, magic, and swordsmanship. He can jump very high and is exceptionally strong and agile for a boy of his age. Despite his age and appearance, Finn seems to be quite strong and athletic; he can be seen wrestling full-grown Marauders, the large grass ogre Donny, and a general variety of monsters and creatures several times his size. Finn is also capable of lifting up Princess Bubblegum, as shown in "Mortal Recoil" when he picks her up and puts her in her bed, and capable of lifting up Marceline as seen in "Daddy's Little Monster." In addition, he was able to lift a tree and hit the giant spider Barb with it in "Web Weirdos." In "Another Way," Finn was able to run around carrying a giant cyclops' eye. Lastly, in "Dad's Dungeon," when he stabbed the Evil Monster in the eye, he was able to lift him up slightly off the ground and flip him into the pit. Being the size it is, the giant Evil Monster should have weighed at least a couple of tons, thus showing how strong Finn is. He also can make his arms and legs bend in inhuman ways, as during the Science Dance and when he uses "spaghetti limbs" (waving his arms and legs, which Jake can also do). In "The New Frontier," it's shown that Finn can make fire only with his hands. Finn is very tolerant to pain as shown in "No One Can Hear You" when the stag broke his legs; he just says, "Whatever." Also, in "The Lich," he was able to break the Enchiridion on his knee. Finn seems to have impeccable balance, as he was able to balance himself on two wheels in his wheelchair in the episode "No One Can Hear You" however he refers to it as "skills."

Mental

Finn has the ability to mentally fight psychic abilities. The first time was against the Lich. The second time was against Goliad, as he was constantly able to manipulate his thoughts in order to avoid revealing the plan to defeat Goliad, allowing Princess Bubblegum to create Stormo. Finn can focus for a very long time as shown in "Still" when he spends hours telepathically summoning an Astral Beast. As demonstrated in "The Creeps," Finn can lock unwanted memories in "the vault," which is later seen in "King Worm." However, this is a normal human ability which is activated if the scene the person had witnessed is too traumatizing for them. Finn has the ability to read and write, and he can also do simple math.

Creative

Besides combat, Finn has displayed many other impressive abilities in handicraft. He has some origami skills, as shown in "Ricardio the Heart Guy," in which he makes Princess Bubblegum a paper crane, as well as in "Marceline's Closet," in which he makes a paper airplane. In addition to that, Finn is shown to be able to construct a sculpture (of the Candy Kingdom) from his saliva, which was also made for Princess Bubblegum in "The Real You." Finn is also somewhat gifted at constructing simple machines, such as the catapult in "The Witch's Garden." Finn writes and draws with his left hand and occasionally with both hands at the same time. He additionally handles his sword with his right hand, suggesting he may be ambidextrous, able to use both hands with equal skill.

Musical

Finn enjoys singing; after swallowing a tiny computer, he gained the ability to Auto-tune his voice on command, although he can sing without Auto-tune as well. Apparently, Finn can also play the flute, demonstrated in "Prisoners of Love," in which he played a short lick before javelin-throwing it at Ice King. Unfortunately, the flute fell apart before it could hit him, so Finn is not seen playing the flute again except as Farmworld Finn at the end of "The Lich." He is also very good at beat boxing as seen in "It Came from the Nightosphere" and "What Was Missing." In "Gut Grinder," Finn tries to play Jake's viola, but Jake says he stinks. Jake even imitates his foot prints and said "I'm Finn the Human and I stink at viola." However, during "Death in Bloom," Finn panicked over what instrument to pick, supposedly because he could not play any of them, and settles for sleigh bells. In the episode "Go With Me," Finn is seen playing the lute. In "Daddy's Little Monster," he is seen playing the tambourine.

Miscellaneous

Finn is very good at playing a video game called Adventure Master, which he and Jake play on BMO from time to time. He can also spit very long distances, as demonstrated in "Evicted!," when he spits on Marceline, in "My Two Favorite People," when he spits on Tiffany's face, and in "Web Weirdos," when he spits at birds flying overhead, while suspended upside down on a giant spider web. In "Dungeon," one of the trials that Jake says Finn would have breezed through is a spitting competition against a goblin-like creature. In "Burning Low," Finn is shown to be able to spit water incredibly high into the air.

Temporary

Finn and Jake gained magical abilities in the episode "Wizard," but they have never used those abilities in any other episode. Pendleton Ward later revealed on his Formspring that all of the magic Finn and Jake gained in that episode was contained in their robes, which were destroyed.

Likewise, in "The Chamber of Frozen Blades," Finn and Jake gain ice-ninja skills, but it's unlikely they will use them again because, according to Adam Muto, "They didn't have enough time to commit the incantations and hand positions to memory."

Relationships

Joshua and Margaret

Joshua and Margaret were the parents of Jake and Jermaine, and the adoptive parents of Finn.

Jake

As housemates, brothers and best friends, Finn and Jake share a very deep and strong bond. Having been raised together by Jake's parents, the duo share a relationship similar to that of siblings, with Jake acting as Finn's older brother. Though they have an unconditional love for each other, Finn can get frustrated with Jake because of his laziness and lack of motivation, shown especially in "The Witch's Garden." As a more laid-back character, Jake often tries to relax Finn's fiery personality in the face of a struggle, advising him not to worry in most situations. Though he sometimes leads Finn down the wrong path, Jake genuinely means well for his companion and is usually an encouraging and protecting figure in Finn's life. Finn and Jake have saved each other's lives on several different occasions, and often adventure throughout the Land of Ooo together.

A unique part of Finn's relationship with Jake, is that Jake is able to tell when Finn is about to cry, as shown in the episode "Freak City" and is stating to be a "mother daughter thing."

Jake and Lady's puppies

Finn also has shown to also like his nieces and nephews as he was happy to meet them in "Jake the Dad" and even wore a shirt which had written upon it "BEST UNKLE" upside down. During the short period of time Finn was with the puppies, he started to play with them (such as when Jake saw him with them he said they're having some "uncle wrestling"). Finn displayed a general apathy to Jake Jr.'s appearance.

BMO

BMO lives with Finn and Jake in the Tree Fort. It serves as their living video game system, film editor, camera, and many more portable electric items. It appeared in the eighth episode of Adventure Time, so it is obvious it had been with them for a long time. In "Video Makers," BMO records the footage requested by Finn and Jake, although they disagree on what genre of movie it will be, so they leave BMO a note that tells it to keep only the best footage and present it at the Movie Club. It ends up bringing them together by using both the action and comedy/romance footage and singing his Friends (song), so it appears it doesn't take sides with either of them. In "Incendium," BMO's video game music inspires Finn to sing All Gummed Up Inside, then BMO helps watch him while Jake courts Flame Princess, and pulls a kancho prank on him. Occasionally, Finn and Jake seem to take on parental roles when it comes to BMO, such as taking it to soccer practice or disciplining it when it misbehaves.

Marceline

Finn and Jake's first meeting with Marceline. Though he initially considers her an enemy in her debut, "Evicted!," Finn quickly befriends Marceline the Vampire Queen, as he learns that her seemingly evil ways are just playful teasing in "Henchman." A rowdy and adventurous character, Marceline and Finn share the same vigor and thirst for danger. One of the key reasons why they managed to forge a friendship is that Finn saved her life in "Henchman" when Jake exposed her to direct sunlight and threw garlic at her in a misguided attempt to save Finn. In the same episode, Finn, in an attempt to convince Jake of her generally wholesome ways, calls Marceline "a radical dame who likes playing games." As previously stated, Marceline loves to mess with Finn's head. Despite Jake's fear of Marceline (and of all vampires), Finn enjoys spending time with her so that they can be "awesome together." In "Go With Me," Finn asks her to go to "Couples-Only Movie Night," but only as a friend. Being (mutually) disgusted to the point of vomiting by the idea of kissing (although ironically she has kissed him on the cheek at least twice), Marceline said no to Finn when he asked her to go to the movies thinking he was asking her to be his girlfriend. In "Marceline's Closet," he accidentally sees her naked when Jake tells him to see if the coast is clear for them to get out of her house, causing him much discomfort.

Lady Rainicorn

Lady Rainicorn, Jake, and Finn Finn became friends with Lady Rainicorn after Jake wanted to hang out with both of them at once in the episode "My Two Favorite People." At first Jake regretted introducing the two, but in the end he was glad it happened. Finn and Lady Rainicorn still share a close bond, despite the fact that Finn can't understand Lady Rainicorn's fluent Korean.

Princess Bubblegum

Finn had a rather obvious crush, which he denied before the events of the episode "Wizard Battle," on Princess Bubblegum, whom he occasionally calls "Peebles" and other nicknames out of affection. He is known to interact with her more than any of the numerous other princesses of Ooo, and would jump at the chance to do anything for her, for which she would occasionally kiss him afterward, though she hasn't been seen doing something like that since "Wizard Battle."

Finn becomes very protective and jealous when someone else comes between them, as seen in "Ricardio the Heart Guy," in which he sought to one-up Ricardio (obnoxiously performing the Science Dance, as a desperate ploy to attract Princess Bubblegum's attention) and expose him as a villain.

In "The Real You," Princess Bubblegum becomes concerned about Finn and his new genius identity after donning the Glasses of Nerdicon. She assures him that she only likes Finn as his normal self. Princess Bubblegum kisses Finn on the cheek for trying to win her heart through his smarts.

Finn eagerly hoped to win the princess over with his heroic deeds. Finn and Princess Bubblegum share a staunch sense of morality and often work together to bring justice and balance to the Land of Ooo. Taking several dangerous and tomboyish cues from Marceline in "Go With Me," Finn tries to set up a movie date with Princess Bubblegum ultimately by trying to "wrestle" her and by leading wolves into her bedroom under Marceline's advice, and the Princess regretfully banishes Finn from the Candy Kingdom until he stops "acting like a psycho."

In "Mortal Folly," when Finn and Jake are chasing the Lich, the Ice King persistently nags them to give him their blessing to marry Princess Bubblegum. When the Ice King says, "It's not like you want to marry her," Finn blushes and angrily throws a rock at him. Earlier in the episode, before embarking on their pursuit of the Lich, Princess Bubblegum gives Finn a pink sweater that she knitted for him, saying that she cares about him. This sweater would later protect Finn against the Lich using the "power of liking someone a lot," as Finn put it. (He later refers to the sweater as his "like-like sweater.")

In "Mortal Recoil," Finn outwardly confesses to the princess that he "likes her a lot," although it is unknown whether she actually heard him, as she was still possessed by the Lich at the time. Princess Bubblegum, whose incomplete reconstruction at the end of season two (resulting from the candy surgeons' inability to completely recover all the pieces of her bubblegum body) caused her to revert to her 13-year-old self, hugs Finn after her recovery and calls him "hero."

In "Too Young," she shows much affection towards Finn. To complete her re-aging process they share "a whopping love-hug" and a kiss. Afterward, she can only remember the hug "was, like, five years ago." Finn feels beaten afterwards, but a pep-talk from Jake brings his spirits back up.

In "Wizard Battle," Finn gets a kiss from Princess Bubblegum again (her last to date) after winning the Wizard Battle. She does this to reward Finn for going to such lengths to kiss her and stop Ice King from kissing her. She slaps him shortly afterwards for cheating.

As of "What Was Missing," it is revealed that Finn has kept Princess Bubblegum's wad of hair from "To Cut a Woman's Hair" and spends quite a bit of alone time with it, as stated by Jake. She becomes aware of this as Finn reveals the secret in his song.

After being rejected several times, in "Incendium," Finn becomes deeply depressed and cries over Bubblegum by a little shrine he constructed made up of two framed pictures of her, his lock of her hair, and a pool of his tears. He becomes enraged and states that he'll kill whoever started a fire that burned his two pictures of Bubblegum. After his brief encounter with the Flame Princess (who started the fire) and saying that he likes her, and later saying that he thinks he has a crush, showning that he has gotten over Princess Bubblegum.

In "In Your Footsteps," Jake says that Princess Bubblegum was his ex-girlfriend, but Finn replies they "never went steady."

In "Burning Low," he thinks Princess Bubblegum is jealous of his new relationship after hearing this statement from Jake; this thought is boosted by her attempts to call off the relationship, but in reality she is trying to prevent global destruction from a disastrous reaction by Flame Princeess's unstable elemental matrix, which would be triggered by extreme positive emotion, including romantic affection. When he goes to write poetry for Flame Princess, Bubblegum finds him, and tries to explain to him that "responsibility demands sacrifice." She says that she's glad they both understand why he can't see Flame Princess; this makes him angry, and he reveals to her that he was formerly in love with her, but because she didn't love him back he is ready to move on.

Flame Princess

Finn first meets Flame Princess at the end of the episode "Incendium." During the episode, Jake poses as Finn trying to court her because he believed that Finn, depressed after being rejected again by Princess Bubblegum, needed a new love interest. However, when Flame Princess's father tells Jake that she is evil, Jake tells her (disguised as Finn) that he doesn't like her, which causes her to become confused and angry and attack him, following him back to the tree fort where the real Finn is. She starts a fire in the house which burns the pictures in Finn's shrine to Princess Bubblegum, and he becomes enraged and runs to see who ruined his shrine. He is surprised to see it's Flame Princess. When she accidentally lights the liquid pyrotechnics left behind by Princess Bubblegum and douses her fire, he saves her and brings her into the house. When she regains consciousness, Flame Princess yells at him, "You! What's wrong with me, huh?! You don´t like me?!" and Finn states, "I like you!" Flame Princess blushes. She then slaps Finn and warns him never to mess with her again, and flees the tree house. After she slaps him, he immediately wanted to know who she was. He then told Jake, "Dude, I think I have a crush."

In the continuation episode, "Hot to the Touch," she officially becomes Finn's new love interest. He asks Jake to help him find her, saying that he "peeped beyond her burning gaze" and that "she ain't evil," and the two run out to look for her. They spied her by a pond and hid behind the bushes to watch her. Finn affectionately likened her to "the steam off a puppy's nose searching for ham in snow" and "a cute little flower." When she curiously dips her hand in the pool and jumps back in pain, Finn rushes to her aid, surprising her. Finn admits to Flame Princess that he really likes her and they should be together, which causes her to glow brighter and makes small fires appear around her. Finn is surprised with the fire getting near him, so he tries to put them out, not knowing that by putting out the flames he would hurt Flame Princess. Angry and confused, she runs again and the brothers chase after her, then she ambushes them. However, the attack does not last long, and Finn confuses Flame Princess by trying to compliment her while she is trying to kill them. He then tries to explain his feelings again which causes her to blush, but she resists. Upset that when Finn makes her glow brighter, he puts it, she warns him that he "should not toy the emotions of a fire elemental." Flame Princess says that fire's purpose is to burn and proclaims that this land (Goblin Kingdom) will be her own Fire Kingdom. Finn tries to convince her not to do it.

She refuses and casts a wall of fire to back down Finn and Jake. When they fly to Goblin Kingdom with fire-proof suits, Flame Princess attacks them with fireballs but they have no effect. She again shoots another fireball at Finn, but this is deflected and instead hit a cart. Jake extinguishes the cart's flames, consequently hurting Flame Princess once more. Finn distresses that he doesn't want to hurt Flame Princess, but his morals say he must help the citizens of the Goblin Kingdom. Neptr, thinking he's helping, engages the foam blaster to extinguish her. However, Finn manages to stop Neptr from directly hitting Flame Princess and instead he hits Jake and a few of Flame Princess' flames, hurting again Flame Princess. Flame Princess then gets extremely angry and proclaims, "That is the last time you hurt me," and grows into her beast form, a towering human-shaped fire. A fiery tear from Flame Princess' right eye is revealed that she is harmed both physically and emotionally. Finn shouts, "No more! No more!" and literally rips himself out of his own suit and stands on top of it, shouting out to Flame Princess. However, he is ignored.

Finn, angry and upset that he can't "just like a girl," begins to cry. A tear of his falls on the flames of Flame Princess, stinging her and catching her attention. Flame Princess watches Finn cry, confused and amazed, then stops her flames and approaches him. She says that now she believes that Finn is a Water Elemental because he "creates water," or cries. Flame Princess says that no matter how much they like each other, they can't be together because they are of conflicting elements. Finn tries to explain that he isn't, but Flame Princess has trouble understanding the concept and says even if they liked each other, they would only hurt each other. Finn replies, "No, I can take it. I mean...we can try." Flame Princess glows, touched that he "would defy nature for" her. She hugs him, and although he smiles for the first few seconds, Finn begins to burn up and pushes her away. Flame Princess then bids him goodbye.

In "Burning Low," she and Finn are dating. She even thanks him for building her house and they hug each other. He decides to go to "tier two (smooching)" after another date, but only receives five hugs, which according to Jake, does not count as "tier two." Embarrassed, Jake then gives Finn the idea to write her a "sappy poem."

Finn and Flame Princess' first kiss Finn also gets angry at Princess Bubblegum for wanting him to stop seeing her. Then, when Jake is convinced what would happen if Finn kisses Flame Princess, he and Princess Bubblegum try to stop it, but arrive to see them already kissing. When Flame Princess falls into the earth's crust due to her instability, Finn goes in to save her, with Jake cutting off her oxygen supply. After using artificial respiration to revive her, they continue to dateIn "Ignition Point," Finn and Jake go to the Fire Kingdom to retrieve Flame Princess' scented candles. He refers Flame Princess as his "lady." After hearing Flame King's words that she might be evil, Finn gains a motivation to change her to good.

In "Reign of Gunters," Finn takes the advice of a dating book called Mind Games and tries to act more mysterious, claiming he needs to keep all the ladies in a state of confusion; that way, he has "options in case Flame Princess doesn't work out."

In "Vault of Bones," Finn knows Flame Princess is good by his heart, so he goes to the Vault of Bones with Flame Princess for prove to her she's good. Together, they traverse the dungeon, with Finn teaching her how to properly dungeon crawl. She thinks her methods are boring, and (due to her destructive personality) she opts to just burn through everything with her elemental powers. However, when Finn is trapped by a Giant Goo Skull, Finn warns Flame Princess not to use fire to defeat it. She instead defeats it the way Finn taught her to—by intimidating it. She assures Finn that she'd never hurt "[her] boyfriend," and afterwards, she says that she had a great time.

In "Puhoy," Finn says that he told Flame Princess a joke, but she didn't laugh, which causes Finn to worry about the status of their relationship. When Finn goes into the Pillow World, he cheats on her with Roselinen. After he returns, Flame Princess calls him, saying that she finally got his joke, and she thought that it was funny.

Roselinen

In "Puhoy," Finn meets Roselinen, his third love interest, in the possibly-imaginary realm of the Pillow World. Finn enters this realm while having supposed relationship problems with Flame Princess to let his mind unwind; when he meets Roselinen, she asks him to dance, to which Finn replies, "I have a girlfriend." She insists that the gesture is purely platonic, and they dance. As they talk, she shows signs of liking him, and Finn talks half-embarrassedly. Eventually (as by this time, Finn believes there is no way to escape the Pillow World), Finn abandons his relationship with Flame Princess to start a new life with Roselinen, having two kids named Bonnie and Jay. When Finn finds out there is a way to escape the world, he is fully willing to go, though torn up about leaving his Roselinen and his family behind. Roselinen asks Finn to not forget about them. When Finn exits the world after dying of old age, he does end up forgetting about Roselinen and his family after a call from Flame Princess.

The Lich

Due to the Lich's desire to kill off life in the multiverse and Finn's status as a hero, the two are always in conflict. They first met in "Mortal Folly" (although it's implied that Finn knew about the Lich before this in "His Hero"), where the Lich is freed from his prison and goes on a rampage and tries to regain his power to destroy all life. In the episode, the Lich tries to dip Finn in his well of power, implying that the Lich believes Finn should be on his side. He also states that he believes Finn is his inferior. 

The Lich was shown trying (and succeeding) in munipulating Finn's emotions to his own gain several times. This was first shown in "Mortal Recoil," where the Lich (disguised as Princess Bubblegum) munipulates Finn's romantic emotions toward Princess Bubblegum and makes him hand over the things he needed to regain his powers and continue his quest to destroy all life in the multiverse. Later, in "The Lich," the Lich (disguised as Billy) grows to be somewhat of a father or a brother figure in Finn's eyes. The Lich uses this and makes Finn get the gems of power, which he connects with the Enchiridion and uses to travel to the center of the multiverse and the wishmaster Prismo.

Ice King

As the story's recurring antagonist, Ice King and Finn are frequently at odds. Finn is prone to impatience and quick aggression around him but can show him sympathy, as in "When Wedding Bells Thaw." However, Finn's aggression never outweighs his compassion, honor, and respect for life, as evidenced when he refused the opportunity to slay Ice King as Billy had slain the Fire Count. Similarly in "Mortal Recoil," Finn, albeit grudgingly, trusted and united with Ice King against their common enemy of the Lich-possessed Princess Bubblegum. Further contributing to their differences, Ice King competes with Finn for Princess Bubblegum, until the closing scene of season two. This mutual attraction for Princess Bubblegum can be clearly seen in "Mortal Folly," where Ice King continually pesters Finn for consent to wed Princess Bubblegum. Upon Ice King's saying, "It's not like you wanna marry her," Finn blushes and hurls a rock at Ice King.

Although Finn and the Ice King started out as bitter rivals, their relationship progressed to a friendly rivalry, then an odd friendship in its own right, and finally a genuine friendship.

The Ice King does not really hate Finn and Jake, as he only fights with them because they are opposing each other in terms of morals. He frequently tries to be friends with them (in his own, misguided way) and has willingly made alliances with them. In the episode "Still" The Ice king freezes Finn and Jake so they can have "bonding time." It was shown in "Hitman" that while Finn and the Ice King are rivals, they are not enemies, and don't harbor any real malice towards each other. The Ice King made it clear that he doesn't want to kill Finn, the most he would do is punch him in the belly and make him vomit up his lunch. At worst, they are battling rivals, as Finn openly disapproves of the Ice King's habit of stealing princesses and causing mischief. At best, they are playful rivals, even friends. In "Holly Jolly Secrets Part II," the Ice King has a locket with the pictures of Finn and Jake. Near the end of the episode, the two are shown snuggled up side-by-side by a roaring fire, wearing ugly Christmas sweaters. Finn's attitude towards the Ice King has softened since discovering the tragic secret of his origin, and his compassion for people in distress outweighed his petty squalls with him enough to be his friend.

Story of Joining Sora's Team

When Finn, Jake, and BMO were adventuring around for new foes and friends, they met Sora, Goofy, and Donald Duck when they fell out of the Gummi ship. As they met, Finn saw Heartless sneaking up on them and punched the creature, but then it had no affect. Not even his Demon Sword was enough to beat the Nobodies. But when Sora, Goofy, and Donald fought them, they were all defeated and it made Finn, Jake, and BMO want to be stronger than them. When the three asked, Big Yellow managed to cut in and tried to kill them all. When the showdown ended, Sora accepted, but after when find the pathway for the new worlds to connect. When they searched, they met up with Yakko, Wakko, and Dot, who met Marceline, Lumpy Space Princess, and Princess Bubblegum. When the Castlevenoms were attacking the Candy Kingdom, the group hurried and fought them off, and went face to face with The Lich, which caused Finn and Jake in confusion, and Sora figured that Maleficent brought him back to life. Sora, Finn, Jake the Dog, Donald Duck, BMO, Marceline, Goofy, Yakko, Wakko, and Dot engaged to combat, and had a showdown thaat lasted about 109 sec, with help from Ice King, and Flame Princess. After the showdown, Finn and his friends joined the team finally to stop the Lich and Maleficent.