let’s start with DNA. Martin is more than just a reason to explore Finn’s backstory and make him sad and armless. Martin is Finn’s biological dad, which means they might share certain personality traits.
Finn’s alternate-wish-world mom seems like she’s probably a better person than Martin, and Stormo is made from Finn’s “heroic DNA” and shares his mom’s blonde hair, so the most obvious symbolic (not scientific) interpretation is that Finn’s mom is the source of the heroic DNA while Martin is the source of any inherent wrongteousness. whether or not this is true is uncertain; for all we know Martin is a hero in his own way. but for the sake of analysis it’s worth assuming what we’re meant to assume: Martin is Finn’s bad side.
and if there’s one thing we know about Martin it’s that he’s entitled. “The Visitor” presents this as clearly as a fable. Finn, exhausted and dehydrated, politely asks for some water, and later Martin chugs the whole barrel and tosses it to the ground. throughout the episode Martin takes advantage of the villagers while Finn does whatever he can to make the experience less traumatic for them, and what we learn is that Martin is selfish and manipulative and gets what he wants. Finn is the good guy, of course. but he is Martin’s son, and under the right circumstances perhaps they wouldn’t be so different.
when we first meet Finn he’s partying in the Candy Kingdom, raising the dead with Princess Bubblegum and freely taking bites out of the walls and sidewalks. free food is not for everyone, by the way; Finn’s alter ego Davey has to pay for a street vendor’s Coco Birds, whereas Finn can take anything because he’s Finn. as the hero of Ooo and friend of the kingdom’s ruler/creator/all-powerful and all-seeing god of life and death, Finn is spoiled.
and it’s easy to see how the lines between things and people would get blurry for him. candy citizens are sentient food created in labs, and Ooo is a place where trees and mountains can talk and a 12-year-old can become the proud father of a microwave and then battle for custody of the microwave and then abandon the microwave in a pile of junk for 15 months. (yep, he’s Martin’s son.) so when princesses made of slime and hot dogs want to marry Finn, what’s stopping him from seeing those princesses as objects to take? everyone wants Finn, and Finn can have pretty much anyone he wants.
except he can’t. “why do i keep trying if i can’t keep her?” Finn sings as he gazes wistfully at framed pictures of Princess Bubblegum. good question, Finn. for the first two seasons he denied any feelings for PB until the opportunity was handed to him at the end of Mortal Recoil. when PB turned 18 again, Finn lost someone he could never admit he wanted in the first place. and now that he’s actually making an effort, fighting wizards to kiss her and nervously squirming his head into her lap, he’s experiencing something unfamiliar and absolutely terrifying: rejection.
it’s no accident that “All the Little People” is so suggestive: Finn stays up late at night simulating debaucherous relationships between tiny versions of his friends, and he can only make things right by shaking his “little Finn” as hard as he can. Finn is frustrated, and when he doesn’t know how to deal with frustration he gets addicted to the feeling of manipulating others. playing god.
Adventure Time loves this motif. i mean really loves it. playing god with the “little people” is a theme that pops up all over the series. Flame Princess references it by name in “The Cooler” which is a reference to when dream-baby Finn echoes the “wawawa” sound in “Frost & Fire” which is foreshadowed by the diaper prank in “Jakesuit”. Magic Man sings about it, and “Astral Plane” suggests Grob Gob Glob Grod and Mars might be involved with it. “The Visitor” is built on this imagery. it’s everywhere in every form. even in that classic gif of Jake saying “we could rule them like gods! angry gods.”
the point is that Martin, PB, and Finn all have this in common: they play god. it’s in Finn’s DNA, and when he couldn’t learn it directly from Martin he got hands-on practice with PB, and he and PB both hurt Flame Princess because they thought they could toy with her. Finn doesn’t notice that PB is doing this to him until “Too Old” when it’s revealed that part of her plan was for Finn’s plan to fail. “Too Old” is a turning point for Finn’s worldview because in one horrifying night it becomes clear that he’s both a pawn and a player in a cosmic game of chess. everyone in Ooo is either eating someone else or being eaten. this is why older people are “less fun inside” and Finn decides to make things right with Flame Princess.
so has Finn changed? in season 2 he wishes for an Ancient Psychic Tandem War Elephant to control with his mind, and then he promptly dumps it in the basement, a lot like NEPTR. in season 6 he sets APTWE free: “i feel weird giving you orders.” Finn has learned a lot, especially since his breakup with FP. if Martin represents Finn’s selfish inner manchild, a “kid stuck in a dad’s body”, then Martin’s escape from the Citadel represents Finn growing up, his carefree childhood violently torn away like his arm, his eternally crystallized youth melting in the flames of existential loneliness and dread. dread doesn’t prevail; Sweet P is born and life goes on. but Finn still needs some time to catch up.
after sorting out the concept of revenge, Finn is left with a wilting flower for an arm, a manifestation of the grass curse that seems to reflect his emotions. Finn is depressed. in season 1 he was desperate to dance with Princess Bubblegum, and now in “Breezy” he’s just sitting with Raggedy Princess at a party and doesn’t even acknowledge that PB is there. but that’s not relevant, right? Finn is over PB and that’s healthy… right? or have his experiences left him with a need to repress his feelings and stuff them into The Vault?
the flower slowly dies as Finn numbs the pain with meaningless pleasure, kissing every princess he can find, until finally it blooms for Breezy. “my love will not fade,” Breezy sings, while Finn sees a vision of Princess Bubblegum. “this memory of feeling… who calls to my heart?” “my hero arise; let love be your guide.” what does it all mean?
Finn loves Princess Bubblegum. he tried to move on and get with Flame Princess, and then he tried to get back with PB, and then FP again, and then every princess in Ooo, but listen: he loves PB. romantically? as a friend? it doesn’t matter. “i see love beyond reason.” Breezy’s unconditional love is what inspires Finn. the epiphany here is a big one: Finn doesn’t have to get what he wants. he can continue to love, just like Breezy. after all, Breezy doesn’t need to be with Finn to appreciate his flower, and Finn doesn’t need to be with PB to feel whatever it is she makes him feel. and what is life without desire? to quote a wise dog: “if you get everything you want the minute you want it, what’s the point of living?” so the flower blooms, the arm is reborn, and life goes on.