In "Trouble in Lumpy Space", there's a conversation where Finn thinks Jake (in the throes of the Lumps) is about to request this of Finn, should he go completely Lumpy. It's never actually stated, and it turns out that Jake just wanted Finn to still be friends with a Lumpy Jake. "What did you think I was saying?"
Parodied in "Holly Jolly Secrets", where Beemo can't press the snooze button for his alarm function himself. It's against his programming.
I Want My Beloved to Be Happy: The overarching theme of the episode "Betty". After the Ice King is reverted back to Simon by a magic-negating entity known as Bellanoche, he uses Hambo as a catalyst to open a portal to the past to speak with Betty and let her go so she doesn't have to suffer from what he went through. She jumps through the portal to the present and immediately takes the initiative to save Simon's life, taking him to Bellanoche, knocking her out since she has no magical powers to take in the first place, and restoring Simon back to the Ice King. At the end of the episode, she silently watches his oblivious self from a window before flying off on a magic flying carpet.
Even prior to Marceline was the Ice King, whose want for friendship was actually a secondary goal aside from princess capture. When Marceline and Ice King finally meet each other, let's just say their pasts play a vital part in the other's want for friends.
I Taste Delicious: Almost said word-for-word when Jake eats a crayon drawing of himself in "The Jiggler":
Jake: "I taste awesome."
Also in "Dungeon":
Finn: "Everybody wants to eat me up. Probably because I'm so sweet."
Finn's reaction to soy-people.
Ice-Cream Koan: The Royal Tart Toter's speech at the Royal Meeting. Justified, as he is very senile.
Royal Tart Toter: "This cosmic dance of bursting decadence and withheld permissions twists all our arms collectively. But, if sweetness can win, and it can, then I'll still be here tomorrow to high-five you yesterday my friend. Peace."
If I Had a Nickel: After he frees Tree Trunks from the power of a crystal apple, Jake tells Tree Trunks if he had a penny for every time someone has been driven mad with magic power... he'd be Abraham Lincoln.
Ignored Aesop: Played dead straight in "What Was Missing". After the group opens the door, the Door Lord refuses to give them back their things. Then they realize that the lesson he wanted them to learn was that friendship is the real treasure, and the Door Lord happily celebrates over their Fridge Brilliance moment. They then proceed to beat the Door Lord to a freakin' pulp and retrieve their stuff anyway. Wow.
In Joke: Several to character designer Natasha Allegri's cat Pancake, both visual and spoken.
Indirect Kiss: In "Burning Low", after Finn and Flame Princess direct kiss caused FP to burn through the Earth's crust, Finn decided to kiss a rock and give it to FP where she also kisses the rock.
Info Dump: Oh boy, "The Lich" can pretty much take the cake. After finding The Enchiridion in the possession of Billy, Finn flips the sword on the cover, revealing pretty much everything about The Enchiridion and how the plot of Season 5 will move forward. Through the explanation of a Motor Mouth hologram named Booko, it is told that the Enchiridion has a secret power when combined with the Gems of Power in the crowns of all Ooo royalty. Needless to say, this explanation comes out of nowhere and floors everyone. Quote: " What you see here is a map of the Multiverse. It shows all known dimensions and the links between each of them. This is the dimension that currently contains the universe in which we currently reside...At the center of the Multiverse is a dimension called the Time Room, believed to be the quasi-coporeal dwelling place of the almighty Prismo! The Time Room is a single dimension that exists outside of time. The Time Room produces the Time Waves that are experienced by other dimensions. Some dimensions have permanent links that allow travel to and fro. Others become linked temporally by naturally forming wormholes, and others can become linked artificially by magical portals, torn open by objects of great power. Once the last gem is inserted into the Enchiridion, it will have the power to create a portal to any dimension in the Multiverse. An activated portal creates a time dilation in which either end of the portal experiences a temporal synchronization allowing for the same passage of particles through a non-local region of space-time!" All this was said in under a minute.
Innocent Innuendo: In "Fionna and Cake" shortly after Cake sends Fionna off alone with Prince Gumball to his room, she begins hearing strange noises that sound suspiciously like rape, but is actually Fionna fighting Ice Queen.
(from far away) Urgh, URGH! GET IT OFF ME! Cake:FIONNA?!
The entire episode of "The Chamber of Frozen Blades".
Instant Expert: Averted when Finn asks the robot swordsman if he can become a master swordsman after their brief duration of practice. The robot replies "Yes, if you keep this practice up for 10 years, and if you gain a robot body like mine." Finn still has a lot to learn.
Inter Species Romance: Jake and Lady Rainicorn. Any romance with Finn is also this by default since he's the last human in Ooo. Maybe.
Invisible Wall: Beemo's video game Guardians of Sunshine has this feature; it represents the edge of the screen.
Invisible Monsters: Forget that; Finn and Jake go through an entire invisible obstacle course in "Rainy Day Daydream" which only Jake could see because it was in his imagination. "A bowl of baby elephants, chainsaws, and doo-doo's flying towards us! JUMP, DUDE!" Soon they come to a completely invisible monster, who can't be seen by either Finn or Jake.
Irony: The fact that a post-apocalyptic world could be so bright, colorful, and happy (most of the time). Pen has pointed this out numerous times.
Irritation Is the Sincerest Form of Flattery: Played with in "In Your Footsteps", in which a bear starts imitating Finn. Finn doesn't have a problem with it until he believes the bear is trying to outright impersonate him. It turns out neither one was the bear's real goal.
It Was Here, I Swear: Repeatedly subverted in "In Your Footsteps". Each time the bear does something strange, someone acts like this trope is in effect, only for it to turn out everyone already believes them.
It's All My Fault: Finn's exact words when his plan to carry the tarts through the Desert of Doom fails.
While to a lesser extent, Jake and the Ice King work this trope. Jake embodied this trope in "Party Animal" and City of Thieves" when he, despite good intentions, did a lot of harm. The Ice King is ultimately a lonely man looking for love who is Not Evil, Just Misunderstood and a Tragic Villain. His actions are extreme but his goals don't involve anything completely evil.
Donny, at the beginning of his episode of the same name.
Marceline's ghost friends, Wendy, Booboo, and Georgy. They didn't care whether Finn and Jake died and actually intentionally attempted to suck out their guts as a joke.
Marceline's ex-boyfriend Ash, from the episode, "Memory of a Memory", big time. He sold Marceline's prized possession, a teddy bear (the one Simon gave to her) she'd had since she was a little girl, to a witch for himself and wonders why she breaks up with him! Plus, he tricked Finn and Jake into making Marceline forget that he's a jerkass.
Jig Saw Puzzle Plot: What happened during the apocalypse and extinction of humanity, and how the bright land of Ooo came to rise from the ashes has been left mostly a mystery. A few flashbacks,mentions, and circumstantial evidence paint a picture: Pre-fall mankind started the "Great Mushroom War"—at first thought to be a Deadly Euphemism for a nuclear holocaust, it turned out that the "Mushroom Bombs" were similar but distinct from nukes (possibly literally powered by evil energies). The specific effects of the Mushroom Bomb are unknown, but preventing one of them from falling would have allowed human life to continue in some fashion for another millenium. The fallout from the mushroom bombs created a Zombie Apocalypse of slimy oozing goo mutants, as well as the proto-Candy People (giant possibly alive globs of bubblegum) which outnumbered other living creatures within a few decades, with slime and bubblegum growing to cover most surfaces. While the present day Ooo doesn't have anything specifically like the goo monsters (at least, you don't see anything like them until they show up in "James"), the Candy People are alive and well.
Just Eat Gilligan: Averted in "The Limit". Jake actually suggests stretching over the maze to skip the obstacles, but Finn points out the sign that says "NO CHEATING OR YOU DIE".
Karma Houdini: LSP could be considered one in "Trouble in Lumpy Space"; she kept making things harder for Finn to help Jake by being a Jerkass and when Finn calls her out she says she was only trying to help and makes him feel bad.
The three Jerkass ghosts from "Heat Signature" who spend the whole episode beating up and humiliating F & J, and don't recieve any sort of punishment for their actions.
Kissing Warm Up: Referenced in the episode "The Enchiridion." Finn opens the eponymous book to examine it and finds a page titled "Chapter 5: How to Kiss Princesses." Pausing the scene quickly reveals that the author recommends practicing on a Lip Monster beforehand.
Kiss of Death: Subverted. A kiss from Death restores your memories.
Kiss of Life: Finn does this to revive Flame Princess in the episode "Burning Low."
Knight Errant: This is essentially what Finn and Jake are, from a folklore standpoint.
He came back only this time in the body of Billy and with a plan to open up a portal to another universe. His actions were so well executed, he literally changed the entire show, from plot to color tones.
Lab Pet: Princess Bubblegum has a lab rat named "Science" who she not only treats like a pet, despite being involved in some of her experiments, but is also trained to actually perform some complex experiments for her.
Lady of War: Warrior Princess. Who later turns into Ghost Princess.
Lame Pun Reaction: The ending of "Loyalty to the King", after Finn reveals the Nice King to be the Ice King by gluing his shaved beard back on.
Finn: Now that's what I call a close shave. Jake:(Shakes his head while chuckling through Face Palm)
Jake: Hey, what kinda coffee do you want? Finn: Hazelnut! Hazelnut! ...What if your name was Zelnut? And then I would be like, "Hey, Zelnut!" Jake: That's terrible... Finn: Hey, Zelnut! Jake:Noooooo! STOP!
From "Reign of Gunters", while the Gunter clones are destroying the bottles:
Jake: Breaking news: that mystery plan of yours is a smash hit. *Laughs stupidly* Because the—of the glass... I guess all they care about is bottles, huh.
Lady Rainicorn's parents thought humans were extinct before meeting him. They might have the right idea, but it's still ambiguous, since they live in the Crystal Dimension most of the time. On the other hand, since they wanted to eat Finn and they regularly dine on a human-flavored soy substitute, they might be in a position to know about this.
In "Beautopia", it's revealed that Susan Strong is most likely human.
"Holly Jolly Secrets" reveals that the Ice King used to be human as well, and likely lived before the Mushroom Wars
Finn is now no longer the only human as BMO's creator, Moe, is still alive and human.
Moe might not be an example; when asked if he was human, he replies "It's human skin".
The Ice King has an entire monologue of this while staring into a blank TV in the tree house during "Beyond This Earthly Realm". All with a completely deadpan delivery while staring directly into the camera.
Ice King: What do you think, Finn? Can we pull back the veil of static and reach in to the source of all being? Behind this curtain of patterns, this random pattern generator. So clever. Right here in every home, watching us from a one-sided mirror. Finn:(beat, Finn stares blankly) Ice King: Oh! Sorry, just wizard-talkin' to myself!
Lethal Joke Character: The pig in Card Wars, as far as Jake is concerned. (In practice, it seems to exist as a highly specialized counter-balance to the largely-unstoppable Corn landtype, which Jake prefers.)
Limited Wardrobe: Played straight and averted. Some characters like Finn and the Ice King always wear the same thing, while others are more varied. Princess Bubblegum especially almost always has a different outfit in every appearance. Justified in Finn's case: he apparently only HAS one set of clothes. When he loses a sock, he is forced to go sockless on one foot until it is found.
"Mystery Dungeon" shows that the Ice King's magic doesn't work in hot environments.
Longer-Than-Life Sentence: In the episode Too Young, The Earl of Lemongrab succeeds the throne from Princess Bubblegum after she was turned into a child. He's a tyrant who routinely gives these kinds of sentences to the candy citizens throughout the episode at the drop of a hat, and when Finn and Bubblegum pull a prank on him his line when sending them to the dungeon has become a meme by itself.
Lotus-Eater Machine/Daydream Surprise: In "Power Animal", Finn is trapped in a machine that is powered by thoughts. He breaks out of the machine and finds that Jake has broken into the gnome kingdom where Finn is being held and they tearfully rejoice. Turns out that the machine is actually working and is one of these.
Love at First Sight: Finn is attracted to Flame Princess the instant he sees her in her normal form.
Love at First Punch: Her angrily slapping him and warning him to "never mess with [her] again" only seemed to intensify this.
"Dude, I think I have a crush!"
Love Confession: In "Mortal Recoil", Finn finally admits that he likes Princess Bubblegum "a lot". However, she probably didn't hear it because of being possessed by the Lich. Or maybe she did... In "Burning Low" in a moment of frustration and rage believing that Princess Bubblegum is trying to keep him away from Flame Princess out of jealousy Finn finally blurts out, "I was in love with you!" This shows Character Development, as Finn has never used the word "love" to refer to his affections for a girl, only "like" and "like-like".
Love Hurts: Finn in a literal sense with Flame Princess, as anything from touching to kissing causes him to get burned.
Love Makes You Dumb: So far, Finn's love for the abovementioned Flame Princess really seems to mess up his sense of judgement, even to the point where Finn was having troubles with his heroics versus his love though he agonizes over this.
Love Redeems: What Finn intends to do with Flame Princess, since her father convinced him she's "evil".
Love Triangle: In "Burning Low", this is subverted for Princess Bubblegum towards Finn towards Flame Princess. It's revealed that PB wanted to get Finn away from Flame Princess for a different reason: Flame Princess is a highly unstable fire time bomb that will go off and destroy the earth from the inside out if she's romanced too passionately.
Luminescent Blush: We dare you to count how many times Finn had this in "The Real You", and for that matter, "Blood Under the Skin".
Flame Princess literally glows brighter when she blushes.
Magic Antidote: In "Trouble in Lumpy Space", antidote for lumpiness isn't in the orb; the orb is the antidote.
Magic Versus Science: "Wizards Only, Fools" centers around this trope, with Princess Bubblegum being against magic (or more correctly, the use of the term "Magic!" to explain away "mystical" things that one does not readily understand), and everyone else being for it, because...well... the characters live in Ooo.
Magic Wand: Xergiok has one. According to Finn they are for wiiimps!
Maintain The Lie: The plot for "Her Parents". Jake has to pretend to be a rainicorn to impress Lady's parents, because rainicorns and dogs are supposed to be enemies due to a war. It turns out that her parents don't care that Jake is a dog, because a dog saved Lady's father in the war.
Marty Stu: Again, in-universe and again justified. Marshall Lee can be considered one, because Marceline's the one writing the fanfiction in "Bad Little Boy".
Maybe Magic, Maybe Mundane: The show has two examples from season 4's "King Worm" and season 5's "Puhoy". The first one being from Finn imagining Peppermint Butler in his magic induced dream. Whether that was the real Pepbut telling Finn he was under the control of King Worm due to him having vast knowledge of dark magic or just Finn's dreaming. The second one is with the Pillow World of "Puhoy". It could simply be a dream of Finn due to his dread over relationship troubles with Flame Princess, or it could be that Finn went to another world, lived there for decades and died, with him somehow being reincarnated into his real world (due to the fact that the fourth season finale "The Lich" explained that wormholes can temporarily be opened and closed at random).
As far as Princess Bubblegum is concerned, magic is in itself mundane:
Bubblegum: All magic is scientific principles presented like mystical hoodoo, which is fun, but it's sort of irresponsible.
Memory Gambit: Finn uses one in "The Real You". In short, Finn was given superhuman intelligence through a pair of nerd glasses. During a science barbecue, he shows off a black hole that threatens to envelop the entire Candy Kingdom. Smart!Finn refuses to stop it, so PB removes them herself. The now-dumb Finn slays the black hole easily with no recollection of his plan, winning PB's heart.
As it turns out, it is even MORE so for the voice actors. John DiMaggio said at a SupaNova 2012 Brisbane (an Australian con) panel that when he is given his script, he is just given numbered lines, completely without context. Thus when he sees lines like "Be calmed by my saliva" and "Yes Finn, just put it in my butt!", he has even LESS idea what's going on than we do.
A Glitch is a Glitch. Every second of it.
"Puhoy" from a subtle, philosophical level. In general, this episode is really hard to wrap your head around though the plot is simple. Let's face it; no child will even begin to understand this episode.
The three-parter, "The Lich"/"Finn the Human"/"Jake the Dog" is a big old bundle of this. Basically, Finn has a dream foreshadowing the fact that The Lich killed Billy and stole his skin. After tricking Finn into helping him, he wishes to destroy mankind, which Finn reverses by wishing that The Lich never even ever existed. They all get wishes in an alternate dimension, by the way. Makes sense? Okay. Because Finn's wish changes all of time, and he turns into a normal boy, with parents, and a normal dog - which is what "The Lich", the final episode of the 4th season, ends. It turns out that the mutagenic bomb never went off because Simon froze the bomb with his ice powers, died under it, and left Marceline (who was never bitten by a vampire, so now ages - though not as fast, since she's still half-demon). Finn steals the crown, uses it to take down a gang, accidentally detonates the bomb, gets Farmworld!Jake turned into The Lich, and is saved just in time by Jake, who wishes that the Lich's wish be that Finn and Jake go back to Ooo, safely. Insane, right? IT ALL TAKES PLACE IN THREE 10-MINUTE EPISODES.
Finn, for harpooning Marceline's touching reconciliation with her father, even though it was awesome.
Also, the Royal Tart Toter in "The Other Tarts", interrupting Finn and Princess Bubblegum's reconciliation hug.
Monster Clown: The clown nurses from "Another Way", who have some sort of foot fetish which they perform onFinn. It doesn't help that he faints and starts having clown nightmares.
Monster Shaped Mountain: The episode "Memories of Boom Boom Mountain", in which the titular mountain is living, has a face, and cries boulders. A female mountain, also with a living face at its peak, appears as well.
As mentioned, Finn slashing and banishing Marceline's dad in the middle of his reconciliation with her daughter.
Happens a little in "Mortal Folly" and "Mortal Recoil": the Lich, Knight of Cerebus that he is, did have a lot of scenes, but there was also a lot of scenes with the Ice King acting goofy and not knowing what's going on, jarring with the scenes of the relatively serious villain.
A good example is in "Morituri Te Salutamus", in which the scenes repeatedly change between Finn violently defeating the ghost-gladiators and Jake happily singing about raising morale. On top of this, the Fight King, like the Lich, is a completely serious villain.
"What Was Missing" starting as a super-silly "write a song" episode. But once Bubblegum calls Marceline's lyrics too distasteful, it becomes a completely serious song where Marceline confesses her feelings about Bubblegum and their past, over a droning electric bass. "I shouldn't have to be the one who makes up with you, so why do I want to?" She backs off once she realizes how confessional she's getting, but DAMN.
Same episode, with Finn's song, which starts out with Finn admitting that he's incredibly self-conscious of the fact that he's younger than all his friends and occasionally questions his friendship with them.
"Holly Jolly Secrets" has this in spades at the end. Silly Ice King antics for the entire episode and then suddenly the Apocalyptic Log of Simon Petrikov turning into the Ice King. Followed immediately by Jake making a joke.
In "Ghost Princess", there is a scene that shows Clarence and Ghost Princess on a date at a Spirit Waves show. When Clarence tells Ghost Princess how beautiful she is, the scene cuts to Finn wildly desecrating graves.
"In Your Footsteps" at the very end. After being followed and copied by a bear for the entirety of the episode, Finn proceeds to tell it off at Jake's behest, causing it to run off into the woods and cry. Luckily, Finn chases after it, and after giving it a heartwarming Be Yourself speech, he hands the bear the Enchiridion, and it merrily goes off on its way (which happens to be straight into the Lich's den, where he delivers the Enchiridion).
"I Remember You" has Ice King singing a love song to Bubblegum, which soon turns into senseless pleas for love directed at no one in particular.
Ice King: Won't someone tell me what's wrong with meee... anybodyy... anybodyy... anybodyyy... (bawling)ANYBODYY!! GROD IN THE SKY, PLEASE TELL ME WHYYY!!
Near the end where it shows a young Marceline and Simon meeting for the first time and him giving her the toy monkey she cherish which quickly switches to the face of The Lich that part of the next episode preview. For a moment there, you believe it was part of the same episode.
The Season 5 two-part opening "Finn The Human/Jake The Dog" switches frequently between Jake having funny conversations with Prismo in the Time Room and Finn's life being ruined, Finn going insane, Finn setting of the atom bomb in Farmworld, and generally all hell breaking loose in Finn'sAlternate Universe.
In "Simon and Marcy", we go from laughing out loud at Simon's antics to amuse Marcy using a broken television to him, and the audience, being suddenly very concerned about Marceline's cough.
The episode "Play Date" raises this trope to an art form. It spends over 85% of the episode playing out a light sitcom-like plot, until the sudden Gut Punch .
In the episode "In Your Footsteps", Princess Bubblegum seems to be very happy with the bear posing as Finn giving her the "Heimlich maneuver". She even knew that it was a bear. She should have backhanded him to next Tuesday. Every episode prior to this shows PB shrugging off Finn's romantic advances, saying the age difference is the main problem. Then a bear grabs her from behind and she's okay with that? Unless... she really wants a physical relationship.
Finn: Okay. So you guys should wish to get your buddies back right?
Hot Dog Knight: I wish for a box! (box appears)Sweeeet!
Murder the Hypotenuse: When Bubblegum found out about Finn's attraction to the Flame Princess, she discovered that FP will become physically unstable if she's submitted to too much romance, which would end with her melting her way all the way down to the planet's core. That scenario does happen, and Finn ties Jake around himself like a rope and jumps in to rescue her. Jake himself ends up getting dragged along and eventually covers up the hole. PB realizes that if Jake stayed there just long enough, the problem would be solved because FP would have no more oxygen to live. It's not that PB was intentionally trying to kill off a potential love rival, but rather trying to prevent a catastrophic disaster from endangering the Land of Ooo.
Mysterious Parent: We don't know who Finn's real parents were, all we know is that Jake's parents were his adopted ones. We also don't know PB's either.
Fanon has it that the apparently-sentient wad of pink bubblegum-like goo in "Simon and Marcy" was a proto-PB that eventually coagulated into humanoid form and became the PB we know, in which case she didn't have any parents.
Never Trust a Trailer: The previews for "The Other Tarts" as well as the title card imply that the Royal Tart Toter would have an important role. He didn't. He showed up only at the end of the episode for the sole purpose of being creepy and delivering an Ice-Cream Koan.
Happened even worse with "Holly Jolly Secrets". The trailer implied several characters would show up throughout the episode. In reality, only Finn, Jake, and the Ice King had prominent roles.
In addition, the previews for season four episode "Burning Low" all seemed to indicate that it would play out as a sordid love triangle between Peebles, Finn, and Flame Princess. It wasn't.
Nice Hat: Quite common in the series. Finn's hood, the Ice King's crown, and Party Pat's fedora are pretty good examples.
To that, let's add Marceline's sunhat in "What Was Missing".
Finn and Jake being tricked by Ash to steal the memory of his and Marceline breaking up. Finn is reasonably ticked off when he finds this out.
When Finn and Jake are trying to teach Goliad how to be a good ruler, they inadvertently lead her to use her powers for evil.
Let's face it, they're pretty prone to this despite their efforts. Jake having Fire Princess released to cheer Finn up only to find she was evil. Not only that but it was later revealed there was a reason she was in her prison in the first place as her unstable emotions could potentially destroy the whole world. Then there's Finn attacking prematurely during the trial with Abe Lincoln who was starting to believe that Magic Man (really Jake in his body. MM had switched them around to avoid capture) wasn't who he said he was. Resulting in Jake getting accidentally vaporized and Lincoln having to sacrifice himself to revive him. Oh yeah and giving the The Enchiridion to a bear who was under The Litch's control.
The episode "The Lich" has this in spades, with Finn spending the entire episode breaking things due to being tricked by the Lich into helping him use the Enchiridion to open a portal to the multiverse, where he escapes into and pulls Finn and Jake with him.
The follow-up episodes "Finn the Human" and "Jake the Dog" carries this on as well. To prevent all the pain and death the Lich had caused, Finn wished for the Lich to have never existed. The end result is an AU!Earth which by all accounts is even worse off than Ooo!Earth. Two beloved characters are killed, one becomes the new Eldritch Abomination and AU!Earth enters a new nuclear fallout. Or at least the area Finn resides in.
In "Frost & Fire", Finn instigates a feud between Ice King and Flame Princess in order to relive an erotic dream, resulting in the destruction of the ice land, displacing the snowmen and penguins, and Flame Princess breaking up with Finn when she realizes the entire feud was his doing.
No Indoor Voice: Lemongrab; Abe Lincoln, the King of Mars in "Sons of Mars" (who is in the middle of an amphitheatre with a dome over it, which might not really be indoors...but the prosecutors at the trial don't seem to need to shout to be heard).
No Infantile Amnesia: Finn remembers an incident that happened during infancy where he boom-boomed (read: pooped) on a leaf and fell backwards into it and no one would help him.
No One Could Survive That: In "The Real You", Finn risks his life by jumping into a black hole. Thankfully, he used his fourth-dimensional sword to make it explode. ...So yeah.
Noir Episode: The season four episode "B-Mo Noire" is this, complete with black and white and dramatic narration.
Non-Indicative Name: There's a character named Gary the Mermaid Queen in "Witch's Garden". She is an animated human skeleton and acts rather bird-like.
Doctor Princess is not really a princess. "'Princess' is just a surname."
There are many kingdoms in the Land of Ooo, but many of them are ruled by princesses, which would actually make them principalities. We have seen kings and queens of Lumpy Space and the Fire Kingdom.
At the start of "The Jiggler", Finn and Jake have just finished an adventure where they saved a "family" composed of a pair of watermelons, sausages, marshmallows and such (not even anthropomorphic, either), which apparently involved rescuing them from an evil citadel, a lot of fire, and Finn swallowing a little computer at some point that now makes him sing in autotune.
In "Prisoners of Love", Jake tries to throw a flute at Ice King that immediately breaks. Jake mentions that he broke it when they "tried picking the lock to that Sad Ogre's heart", an adventure we have not seen and are not told any further details about.
"Morituri Te Salutamus" begins with the last seconds of an incident that somehow involves a giant burger monster, a pile of cute little hedgehog-like critters, and Jake not sticking to the plan.
Played for Drama in "Holly Jolly Secrets," the first time the Ice King wore his magical crown, he was lost in the resulting visions it made him see, and when he took it off, he only knew that he had done something unforgivable that caused his fiancée to leave him forever.
This noodle was later sauced in "Betty" when it was shown that she had left him for... him.
In "Ghost Princess", some ne'er-do-well ghosts were about to fight Finn and Jake, until Clarence showed up; at which point, this exchange takes place:
Clarence: Hold up! These guys are with me. Ghost: A'ight, Clarence, but only because of that one time when I did that thing by accident, and you were cool about it.
In "Hot to the Touch", Finn calls Flame Princess innocent, like the steam on a puppy's nose looking for ham in the snow. Jake responds:
Jake: A guy drops one piece of ham in the snow and he never hears the end of it!!
Magic Man's incident with Margles on Olympus Mons, which is apparently the origin point of his jerkish nature.
Not Quite The Right Thing: In "Ignition Point", Finn and Jake foil an assassination attempt on Flame King. Their feeling of triumph is diminished when they learn that the assassins were just trying to avenge their father and that Flame King and his entire court are evil.
Not Me This Time: One episode has Princess Bubblegum order Finn and Jake to capture the Ice King, even though he objects, claiming to have done "no recent crime." Played With because he did do something, but accidentally.
In "Princess Monster Wife" when Finn and Jake confront the Ice King over the princesses' stolen body parts he says he's not the culprit and he's just as concerned as they are, as the thief might come after his own princess. It turns out this princess is made from the body parts of different princess, he was the culprit and he thought they were talking about another body part thief.
Not Quite Dead: Happens twice with the Lich. The first time, he is defeated by Finn and his sweater, but he body surfs into Princess Bubblegum, who is accidentally dropped into the well of toxins by the Ice King. The second time, while taking control of Princess Bubblegum's body, he is frozen and shattered. No dice. He body surfs again into the waving snail.
We see Me-Mow fall off a cliff after Wildberry Princess' body explodes. Me-Mow somehow hitches a ride on a bluebird, thus preventing a messy end.
Not What It Looks Like: Happens in "Fionna and Cake" when Cake finds Fionna with Prince Gumball in his room in front of his bed with her dress torn.
Nuclear Nasties: "Simon and Marcy" shows us just how bad things were during the early days after the Mushroom War devastated everything, including mutations that were leaking glowing green goop from orifices in their body where eyes, ears, noses, and others should have been.
Finn: I thought Snow Golems and Fire Wolves hated each other... Jake: Oh yeah, bigtime. Finn: But they learned to get along... Jake: Yep...
Flame Princess and Cinnamon Bun bond over their mistrust of Princess Bubblegum. She's nicer to him than Bubblegum and he's completely honest with her, unlike Bubblegum or anyone else for that matter.
Off Model: Many fans complained that Jake was this at the beginning of "Crystals Have Power".
Used intentionally in "King Worm"— during the dream, the ears on Finn's hat are longer than normal, returning to regular length when he wakes up.
Some parts of "Up A Tree" tend to veer into this; Finn's face seems to shrink to a third of the size of his hat in some scenes.
Off with His Head!: Finn does this a lot in "Morituri Te Salutamus" to the gladiator ghosts.
An Offer You Can't Refuse: In "To Cut a Woman's Hair", a tree witch threatens to kill Jake if Finn doesn't get her princess hair.
Official Couple: While Lady Rainicorn and Jake were just flirting cutely in the pilot, in the series, they're officially dating.
Finn and Flame Princess appear to be this as of "Burning Low."
Not anymore after Frost and Fire.
Offscreen Moment of Awesome: The epic battle between the Lich and Billy for the fate of the world. All we saw was the brief snippet in Billy's Song, which consisted of Billy kicking the Lich into his castle. Considering the Lich ultimately ended up in the Candy Kingdom being pummeled into a tree so hard he was sealed in amber (which we don't see either), it's clear the rest of the battle was likely extremely awesome.
Finn, Jake and the Ice King's ninja fight in "The Chamber of Frozen Blades".
The Ice King's wizard fight in "Reign of Gunters":
Ice King: I wish I could tell you more about it, but wizards only, fools. Keep it tight.
In "Earth and Water", Flame Princess and Cinnamon Bun overthrew the Flame King and locked him up.
Ice King: So, what did you think of the fanfiction I wrote about you guys? Finn:(beat) Uuuuuhhhh...
Older than They Look: Princess Bubblegum, through a combination of Word of God, Fridge Logic, and an off-side hint in one specific episode, despite the fact that "Too Young" could lead one to think she has a normal aging process. Pendleton Ward once said of Peebles that "the question is how long she's been 18," and the episode "Princess Cookies" shows PB showing up at a candy orphanage in a flashback by an adult candy citizen, looking the same as she does in-series.
Ominous Owl: The Cosmic Owl at the end of the Croak Dream. This refers to the fact that many religions see the owl as an omen of death to come.
Ominous Visual Glitch: The CGI episode "A Glitch is a Glitch" has Ice King installing a virus on the universe's motherboard, causing everything to glitch uncontrollably.
Once an Episode: In every episode, there will be a snail that is waving to the audience. Or at least his shell.
A Lich-possessed Princess Bubblegum does this once the Lich regains his true power. He's powerful enough that he beats the tar out of Finn, Jake, and the Gumball Guardians of the Candy Kingdom with no effort, requiring an Enemy Mine with Ice King.
He wasn't at full power yet. He was planning to regain it after he wrecked the Candy Kingdom.
Our Vampires Are Different: They only drink blood because it's red; Marceline actually sucked the color out of a strawberry in her debut episode. When starving in the episode "Red Starved", she drained Princess Bubblegum , calling it 'low-grade red', but sufficient to get her out of starvation. This left Peebs looking like chewed up gum; pale, wrinkly and thin, but unharmed and quickly restored with the Spoon of Prosperity.
Overnight Age-Up: Rainicorns age faster than dogs. Over the course of two days, Jake's children were older than he was.
Paper-Thin Disguise: Finn, Jake, and Tree Trunks' disguises in "Apple Thief" (if they can even be called that). They just cover themselves in dirt, and the bartender that they met not 30 seconds ago doesn't even recognize them.
Somewhat literal in "Daddy's Little Monster" when Finn disguises himself as a demon using a mask made out of a paper plate.
Pass the Popcorn: Parodied with Jake eating a single piece of popcorn (while in his tiny form) throughout the entirety of "Love Games"; needless to say, all the amusing events in the episode warrant it.
Jake: This popcorn's not gonna last all day! (shrinks) Okay, now it might.
Percussive Maintenance: Used on a gauntlet, only for it to then turn out to be a living thing that feels pain.
Planet of Steves: Apparently, all The Iceking's penguins are named Günther or at least something similar.
Playing Sick: In the original storyboard for "Storytelling" Jake is not really sick. He only does says so in order to make Finn leave so that he could stay at home doing weird things while no one was looking.
This also includes the aptly-named Flame Princess, who embodies this trope with a touch of evil.
Plot Hole: At the end of "Hot to the Touch", Flame Princess goes away from Finn because she decides they're incompatible. At the very beginning of "Burning Low" (her next episode) she and Finn are dating and are on good terms. Also, she's run away from home for some reason. What happened?! This is one of the drawbacks to having only eleven minutes per episode...
Poor Communication Kills: In "What Have You Done?" because Bubblegum doesn't adequately explain what the Ice King did and just says he "didn't do anything" Finn thinks he's going to be punished for no reason and sets him free.
In "Burning Low", Jake falls asleep while Princess Bubblegum tries to tell him why Finn shouldn't go out with Flame Princess. He assumes that PB is just jealous, and learns almost too late that PB was really trying to tell him that Flame Princess' elemental instability would cause her to destroy the planet if she is kissed.
In "The Lich", if Finn actually bothered trying to ask PB for the magical gem in her crown rather than just try and outright steal it, the ending of that episode could have been avoided.
Psycho Serum: The Ice King's magic crown is sort of like this. Gives you tremendous magical powers of ice & snow, makes you immortal at least in the sense that you don't age normally... also it turns you blue, makes your nose and beard grow, and slowly drives you insane.
Psycho Strings: Happens in "Mortal Recoil" for the Lich-possessed Princess Bubblegum when Finn leaves the room.
(Scorcher appears behind Ice King) Ice King: Whoa, you are fast. (beat) Ice King: And quiet. (beat) Ice King: And very good at dramatic silence, I like it...
Ragnarok-Proofing: A lot of ancient junk from the pre-Mushroom War era has survived just fine for a thousand years, often like it had been wrecked only yesterday.
Raised by Humans: At one point, Finn The Human tries to raise a baby Jiggler. His heart's in the right place, but he doesn't know how to take care of the Jiggler and nearly kills it. He ends up bringing the baby back to its mother.
Raised by Wolves: "Memories of Boom Boom Mountain" reveals Finn was abandoned as a baby and adopted by Jake's parents.
Half of the plot for "The Monster".
Rapid Fire No: Finn delivers one in "The Chamber of Frozen Blades".
Finn also does one in "Hot to the Touch" after Flame Princess accuses Finn of having crying as a power.
Rapid Hair Growth: Averted and played straight. In "To Cut A Woman's Hair", after Finn learns that he doesn't specifically need princess hair to save Jake from a witch, he cuts off his Rapunzel Hair (which, incidentally, was revealed for the first time in the series). From then on, whenever his hair is depicted, it shown being slightly longer than the last time it was last seen. Then in "Davey" (which was three seasons later), he cuts it again to adopt a disguise. By "A Glitch is a Glitch" (which was only a few episodes later), his hair's back to the sheer length it was when it was first revealed.
Rapunzel Hair: Princess Bubblegum, Marceline and both Finn and Fionna have really long hair.
Read The Fine Print: The Pledge of Ultimate Responsibility, which Finn undertakes, not realizing it involves holding an asteroid at bay for the rest of his life
Real Dreams Are Weirder: Season 4 episode "Worm King" manages to be surprisingly realistic in its portrayal of dreams. Finn and Jake randomly change location without question or comment (mostly) while hugely strange things initially only make them suspicious as though they can't put their finger on what's wrong. Waking up into another dream makes them think they've woken up for real until they look in a mirror, a common way for people to notice they're dreaming in real life and become lucid because the brain doesn't know what it looks like in a mirror and presents a deformed image. Finn summons things by stating that they will occur. The random nature of the surrealistic events that occur and how they flow into one-another is very close to dreams in real life. And it is very, very weird.
Real Life Writes the Plot: Since Finn's teenage voice actor is developing a deeper voice, the writers decided to age up Finn from 12 to 13. They have also slowly introduced more mature themes like romance.
Finn: If there's anything I've learned today, it's that I am awesome at talking to ladies. And lady, you are CRAZY UGLY! Having beautiful hair isn't gonna get you anywhere because you're ugly inside and out. So ugly, I want to throw up. No one will ever find you beautiful. EVEEERRR. And it has nothing to do with the old chrome-dome. (touches his heart) It has to do with what's in here.
Subverted with Jake to Bubblegum in "Burning Low", as his yelling at her turns out to be completely unjustified and based on his own wrong assumptions about her feelings. (To his credit when she yells at him right back he accepts it.)
Jake:You heartless monster! Do you have any idea how much he's CRIED OVER YOU?! Finn DESERVES to be HAPPY! Even if his BLOOPIN' face gets BURNED OFF! You should be ASHAMED!!!(throws pancake mix at PB)YOU'RE SICK!!!
Really 700 Years Old: In "The Vault, it is revealed that Princess Bubblegum is not only the ruler of the Candy Kingdom, but helped build it. She has been alive for at least a few hundred years and created everything in her kingdom with SCIENCE, including the Gumball Guardians. Finn discovers this in a past-life regression session, and calls her out on it: "PB, you're like a bazillion years old. You're not freaking nineteen! What the heck?!"
In Adventure Time: Explore the Dungeon Because I DON’T KNOW!, which was written by Pendleton Ward (making it canonical) she is given a final age of 827.
Ret Gone: Finn tries to invoke this on the Lich in "Finn The Human" but it ends up backfiring...
Retired Badass: Billy. How Badass was he? He killed an evil ocean... by PUNCHING IT! Still not sure? Princess Bubblegum says Billy didn't just imprison the Lich in amber, he did so by pummeling him into the tree.
Royals Who Actually Do Something: In one episode, Finn becomes king of a goblin city. He tries to be this, but the rules of the city force him to essentially be a figurehead.
Princess Bubblegum probably counts, as she actively worked to fix the plague the Ice King accidentally caused and betters her kingdom through her scientific research.
RPG Elements: Levels, cursed objects you can't take off etc. More DnD-style than video games, and tends to only be minor elements that are only important for the episode.
Finn: So let me ask you a question only the real Jake could answer. Who is always next to me in my recurring elevator dreams? Jake:(immediately) A half-orc shaman. Finn: Okay, you're Jake.
Another example would be when Finn and the Flame King discuss his daughter, and Finn suggests she might be 'Chaotic Neutral' rather than evil. Flame King responds that she might take a penalty to experience if she acted out of alignment, but could be changed to good.
Rule of Three: In 'Princess Potluck', the squirrel from 'The Duke' shoots (and misses) Jake twice before getting a hit.
Rule 63: Character designer Natasha Allegri came up with the idea of what it would be like if Finn and Jake were girls, named Fionna and Cake. Other bent characters include the Ice Queen, Prince Gumball, Marshall Lee, Doctor Prince, and Lord Monochromicorn. And it all started off from her occasional visits to /co/'s Adventure Time drawthreads. Later canonized in the episode "Fionna and Cake."
Runaway Train: At the end of "Mystery Train", Finn accidentally smashes the controls of the locomotive, resulting in the train running out of control towards a broken bridge.