Finn: I shall conquer my fear. Fear Feaster: Yeah, right... Finn: I will! I'll conquer my fear! Fear Feaster: Of cooouuurse you will, and I live in a two-bedroom apartment that doesn't smell like vomit. Hahahahaha, sarcasm...
Scenery Censor: A more literal example for the scenery itself: F&J have a painting of a woman in the treehouse with a large ripped section, which alludes to possible nudity underneath. That said, Word of God indicates that she isn't naked after all.
Schizo Tech and Scavenger World: Up to Eleven on both counts, and justified in that this show takes place after a nuclear war that wiped out technology and made everything into a magical fairy tale world.
The Lich was sealed away in amber by Billy, and it was for the good of everyone, as the Lich is an Omnicidal Maniac seeking to destroy all life. He mind controlled the Easter Egg snail and got free.
Marceline's Dad is the ruler of the Nightosphere, which also appears to be the original home of the Abadeer family (family photos of Marceline, Hunson Abadeer, and Marceline's mom can be seen inside their home; Hunson also wanted Marceline to take over ruling the Nightosphere because it's the family business). The only catch is that Hunson is unable to leave the Nightosphere without outside assistance, playing the trope straight, except with an added Luxury Prison Suite angle.
Bouncy Bee, Honey Bunny, and Sleepy Sam from "Guardians of Sunshine".
Orgalorg is an evil abomination sealed within an adorable penguin.
Sealed Evil in a Duel: Stormo, a Candy Spinx created from Finn's DNA to combat the evil, power mad Goliad, traps Goliad in a psychic duel for all eternity.
Secret Diary: Or it is secret until Finn and Jake find it in his (the Ice King's) room.
Jake's son T.V. finds one and becomes obsessed with it. Turns out it used to belong to Nurse Poundcake.
When Marceline is tied up and about to be killed by the sun, she orders Finn to destroy hers.
In terms of creepiness. Name anything creepy about this show—the Mind Screw ending of "Tree Trunks" and "Evicted!", the Nightmare Faces Marceline, Peppermint Butler's desire for flesh—it doesn't matter. ALL of that was topped by this.◊ Holy. Freaking. Crud. According to Adam Muto, this is just the beginning.
They did it again with those three freaking scary fruit witches in "Dad's Dungeon", two of whom ate the third voraciously.
Then outdid all that with the entirety of "All Your Fault," also known as Amnesia: The Lemon Descent.
A separate example from above from the Season 5 two-part opening: How much worse is it going to get for Alternate Universe Finn in Farmworld? First he is forced to sell his pet to pay back a gang, then tries to find a way around it, then comes across the Ice King's crown which an elderly and insane Marceline warns him to avoid, then gets it stolen by Big D, the gangster threatening his dad, then finds that while he was fighting Big D to get it back, the gang set his hometown on fire, then goes home to find that his house is burning with his family in it, then in desperation puts on the crown, which saves his house by freezing it but drives him insane, then he tries to stop the town from burning and sets off the atom bomb,then finds his family but has to send them away so he can't hurt them (even though they are probably going to die of radiation in the next few hours), then finds that he's killed Jake with the bomb as he's in a pool of radioactive goo, and then has to fight him as he is turned into the Lich via radiation. It would presumably get even worse had Jake not cut it off by wishing them back home.Nice Job Breaking It, Hero!!
In the finale, the conflict between Bubblegum and Gumbald is painted as White vs. Grey when he is shown capable of making peace. Then GOLB shows up, shifting everything hard toward black and white.
Shadow Discretion Shot: Is used in "Escape From the Citadel" when The Lich unwillingly grows back his flesh when Finn flings some Ancients' blood at him.
"Shaggy Dog" Story: "Box Prince." Finn goes to great lengths to assist a cat prince in retaking his cat kingdom...only to have everyone (including the prince himself) just wander off indifferently when it's done. It's a kingdom composed entirely of cats. They don't care.
Finn: Is this...is this even a kingdom?
"Blank Eyed Girl." You never find out what the hell they are. That's part of the beauty.
Shameful Shrinking: Jake used his shapeshifting powers to do this literally when attention was called to him for the fact that it'd been his words that caused Finn to make a party uncomfortable.
Marceline dispels any implications of her getting with Finn any time soon in "Go with Me".
In "Too Young", PB turns 18 again. She says that Finn should just move on because "That was 5 years ago!" Which is even more spiteful than the above example, considering the episode up until that point was Ship Tease upon Ship Tease. Issue 8 of the comic directly references this Ship Sinking and plays with it.
In "Fionna and Cake", Fionna sinks the Fionna/Gumball ship when she realizes that she's not interested in dating him.
Flame Princess dumps Finn for "betraying" her in "Frost & Fire", then proceeds to act ambivalently toward him in "Earth & Water". In "The Red Throne", she reiterates that because of his "betrayal", Flame Princess no longer loves Finn in any way. The ship was finally sunk in "Breezy", when Doctor Princess mentions Finn doesn't talk to Flame Princess anymore, possibly due to Finn thinking Flame Princess is dating Cinnamon Bun after the events of "The Red Throne". Eventually FP and Finn reconnect, but the ship is still seven leagues under.
Word Of God sank the Flame Princess x Cinnamon Bun ship, stating their relationship was strictly platonic.
Shrinking Violet: Raggedy Princess. She spoke for the first time in the series to Finn in "Mortal Recoil" when she brought him his new backpack.
Shock Collar: Lemongrab has his subjects wear them in "Too Old".
Shut Up, Hannibal!: Brief one given by Finn to the Lich, which snaps Finn out of the Lich's mind control.
Lich: Aren't you cold, Finn? Finn: ...NO, I'M NOT! I'VE GOT A SWEATER ON!!
Another in Deep Purple, when Sheryl the Super Porp mascot is explaining her plans to turn the kidnapped child into her successor. Susan uppercuts her before she can finish.
Similar Squad: Billy, when compared to Finn. His main adversary was the Fire Count, from whom he rescued a Cotton Candy Princess, and he had a magical dog. To top it off, both got hair as a gift from their respective princesses and both fought the Lich.
Shermy and Beth, the Pup Princess, fill the roles of Finn and Jake 1,000 years in the future.
Single Tear: The Ice King has one at the end of "What is Life?" As of "Reign of Gunthers" and "I Remember You," both Gunter and Marceline have one respectively.
Played for Drama in "Everything Stays." When Simon has decided he can no longer be with Marcy without endangering her, he tries to wipe a single tear from her face. It instantly turns to ice, slicing a cut in Marcy's cheek, scaring Simon and making him scamper away all the faster.
Sinister Geometry: Subverted in the Soft People, the Cube People, and Spiky People. They're actually pretty nice, but the Spikey People love group hugs.
A bikeless example can be seen with Marceline in the episode "Go With Me" where she and Finn go running with wolves, and when hey stop, Marceline does a pose that pays homage to this trope.
There's an animated gif where Finn was mounting Jake as a motorcycle making this pose, even appearing on Crunchyroll's article. However, it's confirmed this is a fanart gif instead of coming from the series.
Sliding Scale of Continuity: Level 4. While in the beginning the show qualified as Level 2, it upgraded to Level 3 once The Lich and the Ice King's backstory were introduced. It was bumped up again to level 4 in season 4, when the show began featuring more multi-part stories, Call Backs and Sequel Episodes.
By season 6, it's hit level 5. If you haven't seen certain episodes, references to Ice King and Marceline's relationship, Finn's dad, Farmworld, the Lich, the Mushroom War, Betty, the Mars arc, etc., will make no sense at all. An interesting case in that Adventure Time doesn't actually have one single Myth Arc, just a lot of very complex lore.
Princess Bubblegum: I hope you grasp the full consequences of breaking promises. Finn: Heck yeah! If I break a Royal Promise, I get to fight zombies, throw slumber parties, awake Gumball Guardians, and — and — Princess Bubblegum: All right, all right! Finn: — and REVERSE DEATH ITSELF!
Spaghetti Kiss: Happens with Little Finn and Little Flame Princess when Finn gives them a cookie to share in "All the Little People".
"Fionna and Cake" had every character who appears in the opening replaced by their gender-swapped counterpart. Even the singer of the theme song was changed from a male one to a female.
"A Glitch Is a Glitch" gives us the opening completely CGI animated.
The "Stakes" mini-series has a Marceline-centered opening, with her singing the theme song. Significantly, it also incorporates developments in the previous episodes of the seventh season, namely the King of Ooo taking over the Candy Kingdom and Princess Bubblegum living in exile in a cabin.
"Islands" and "Elements" both do the same, foreshadowing the events of the miniseries and highlighting their main characters.
The finale, "Come Along With Me," continues the tradition, with an opening starring Shermy and Beth, year-4,000 versions of Finn and Jake.
The [[Minecraft]] episode "Diamonds and Lemons" has one done entirely in pixel art, by Paul Robertson.
"Weird Al" Yankovic as the Banana Man in "The New Frontier", though he spoke mostly in grunts. He appears again in "We Fixed A Truck", this time with a lot more lines, and he even gets to sing at one point.
He gets another appearance—and song!—in "President Porpoise is Missing!".
Spoof Aesop: Taken pretty much any Aesop the show presents, a more blatant example is a wizard turning people into body parts and not turning them back until they realized how much of a jerk he was. The message here ("some people are jerks and not worth your time") isn't necessarily a joke, but it's pretty pointless considering you can't tell if someone's going to screw you over until you try to help them out.
In "When Wedding Bells Thaw", Ice King almost gets married to Old Lady Princess, but it turns out he had cursed her so she would marry him. Finn and Jake foil the marriage, and it's back to capturing princesses for the Ice King.
Also occurred in "Too Young", when Princess Bubblegum, who was transformed into a 13 year-old at the end of the last season, had to be transformed back into an 18 year-old to reclaim the kingdom from the Earl.
In the two parter, "Finn the Human" and "Jake the Dog" the whole universe goes awry and creates another timeline in which Finn and his human family live in Farmworld and are tormented by the Destiny Gang. This goes as far to the point where Finn has the Ice King's crown and Jake becomes the/a Lich due to the atomic bomb before Prismo encourages Jake to wish that the Lich wishes them back to Ooo.
In "Jake the Dad", Jake decides to live with Rainicorn to raise their pups. Turns out Rainicorn's species matures very quickly. Jake moves back in with Finn since his children are full-grown and don't need him to take care of them anymore. Plus all his stuff is with Finn anyway.
In "Breezy", Finn's right arm grows back with the help of the eponymous bee. Of course, that was far from the end of it.
The "Stakes" miniseries begins with Marceline being cured of her vampirism and ends with her becoming a vampire again.
There's a Wilhelm scream at the very end (right at the cut to black after Finn and Jake are seen on the dolphin's back) of "Memories of Boom Boom Mountain".
Finn's high-pitched screaming from "Burning Low" becomes a running gag in later episodes.
Stock Visual Metaphors: In "Breezy", LSP and Finn make out and she says she is going to take him to "the deep end". A few scenes later, Finn grows his arm back, which replaces the flower that was at the end of his stump. In other words, he was "deflowered".
Parts of "Adventure Time With Fionna and Cake" are written like a Fan Fic. Because it is.
The show's character designs fit this. Pen's artistic style calls for everyone to look extremely simplistic and lazily designed (almost a laid-back style) with no joints for characters' noodley limbs and faces that could be summed up as "two dots and a line". The storyboarders just roll with it and still manage to make everything look pretty damn impressive.
Most of the rapping in the show is not very impressive, but the characters believe that it is, so the whole thing works.
A lot in the first season, before the post-apocalyptic setting was fully obvious. The episode "Tree Trunks" may have had some concerning death, senility, and aging (it certainly spawned multiple theories about how the show was a dream playing out Finn's psychoses and subconscious fears, so there's something there). "The Jiggler" also had a lot about parental abandonment. In general, the show's love of Does This Remind You of Anything? combined with Finn's status as a young, traumatized orphan leads to a lot of unsettling imagery.
It's very apparent in the season 4 premier, "Hot To The Touch." The entire episode consists of Finn running doggedly after Flame Princess because he "like" likes her while Flame Princess is trying her damnedest to make Finn pay for "hurting" her and toying with her emotions (which was Jake's doing, no less). In what has to be one of the show's sadder moments, Finn defeatedly asks himself why he can't just like a normal girl while breaking down into tears. This seems to grab Flame Princess's attention, who (mistakenly) believes Finn to be a water elemental; hence why even if the two did care for each other, they could never be together because they'd only hurt one another. Anybody who's ever loved someone that either just wasn't good for them or hurt them badly can understand this very adult problem and will probably shed a tear or two when they see it for the first time.
Subverted Catch-Phrase: In "Slumber Party Panic". Finn says "What time is it?" to Jake, who questioningly replies "Adventure Time?" Finn replies, "No, it's time for Seven Minutes in Heaven."
Suddenly Obvious Fakery: In "Red Starved", Finn starts searching for a red object for Marceline to suck the color out of, and his search leads him to a creature with a large ruby. Finn requests the ruby, which the creature insists is an emerald before giving it to him. Once Finn returns to Marceline and Jake, Jake also tells Finn that the ruby is an emerald. After Jake explains that Finn must be a little colorblind, the "ruby" changes to green to indicate that it is indeed an emerald.
Sufficiently Analyzed Magic: Princess Bubblegum vehemently denies the existence of magic, and attributes all its properties to specifically applied scientific principles. This gets her in hot water with the very large wizard community.
Summon Bigger Fish: In "Hitman", The Ice King hires a hitman to literally hit Finn and Jake for grounding him. However, when Ice King is told that the hitman would actually kill Finn and Jake, and is unable to call him off, he hires a hit-hitman to take out the first hitman. Surprisingly, this results in a Curb-Stomp Battle with the first hitman easily killing the hit-hitman, making this a subverted trope.
The songs and/or musical notes Finn and the others start with tend to sound horrible and have lyrics that don't make any sense whatsoever, like how someone who was trying to make up a song on the spot would actually sound that's more likely to occur, as opposed to songs that conveniently sound great and have meaningful lyrics.
In "Storytelling", when the wizard realizes Finn has actually improved the forest animals' lives by disrupting the natural order:
Finn: So does this mean I get to go free? Wizard: Your cage is made of sticks, Brother. Just kick it apart.
Unusually for the hero of a children's cartoon, Finn actually ages like a normal human. In the Season 1 episode "Tree Trunks", Jake tells Tree Trunks "Finn can handle it. He's twelve". In the S2 finale, Finn says "13? That's how old I am!" And then we have "15 YEARS AGO", "I'm 16!", and so on...
The Ice King is under a curse that acts as a thinly veiled Alzheimer's metaphor. Despite the show being exactly the kind of setting where The Power of Love and The Power of Friendship should prevail in that situation and recover his mind... it doesn't. Just like with real Alzheimer's patients, no amount of reminders or familial caring can make him recognize his loved ones or remember the person he was, and it only ever ends with the loved ones in tears and onlookers either baffled or starting to cry themselves.
In "Davey", Jake tries to make Finn quit being Davey by dressing like a robber and robbing someone. Instead of breaking character and being a hero, he calls the police and Jake gets arrested.
Several episodes show that Finn's Precocious Crush on Bubblegum is immensely painful to him. Unrequited love hurts even if you're still friends with that person, and despite starting a relationship with Flame Princess, his feelings don't magically go away. They still linger despite his best efforts to move on.
In three words, the end of "Lady & Peebles" shows a common consequence of long term relationships that most children's shows rarely mention: "I am pregnant!"
When Finn and Jake ask Anne if she's seen any suspicious characters coming into her pharmacy, she points out to them that there are so many people who come in and out on a daily basis that the odds of her picking out a specific one as suspicious and remembering them are very low. Subverted when she does exactly that anyway.
When Finn and Jake chase a suspect into a train station, they get arrested for trying to board without a ticket.
In "Lemonhope", the titular character repeatedly refuses to rescue his siblings from the tyrannical Lemongrab despite the urging of Princess Bubblegum. Eventually, the guilt causes him repeated nightmares, so he finally fulfills his destiny, defeats Lemongrab and is apparently set to become Castle Lemongrab's new Earl... only for him to leave again, since he only did it to get rid of the nightmares. Doing something to soothe your conscience doesn't turn you into a hero.
The episode also works on showing what a supposed Kid Hero would do when given that kind of heavy responsibility. In reality, not every kid is going to be like Finn, who is all for helping people no matter what. Instead, some are going to be like Lemonhope, who hated his supposed destiny and only wanted the freedom to live like the kid he is. The sole reason he fulfills it in the end is not because he felt it was the right thing to do, but because he didn't want to deal with the weighing guilt any longer. He just wanted his carefree life back.
Jake: The bazooka goblin has you in its sights! Finn: HEY! Don't shoot us with that bazooka! Bazooka goblin:(giggling) Finn: Don't you do it... Bazooka goblin:(still giggling) Finn: DON'T DO IT, MAN! Bazooka goblin: Hehehehe... (beat) Okay. Finn and Jake: Haha, YEAH! (fist pound)
Symbolic Blood: The Jiggler's juice in the title card for "The Jiggler".
Take a Third Option: In "Another Way", Finn comes to a fork in the road, and is given the choice to go down a path that will make him lose his hair forever, and a path that will make him smelly forever. What does he choose? His way: going through the thorn bushes in the middle. In fact that episode is entirely about that in that Finn sets out on his quest 'because' he'd rather take the third option, further the episode both subverts this trope briefly and then plays it straight towards the end.
Take Over the World: Ice King's goal in "Loyalty to the King". The Lich also qualifies, but to a more dark extent.
Take That!: Season Four introduces "Mind Games", a book that is clearly a Pick Up Artist manual. Ice King knows about and uses it, Jake has it for a joke, and when Finn starts taking advice from it, Jake is (rightfully concerned.
Talking Animal: "Storytelling" shows that most if not all animals are capable of speech.
Jake: But dad, Finn's already figured that out. He's a good kid with a kind heart. Joshua: Remember, Jake, this is a pre-recorded holo-message. I can't hear you if you're talking to me right now. (Moments later...) Jake: But— Joshua: BUTTS ARE FOR POOPING!
It's not a "tape" exactly, but in "Is That You?" Prismo has a conversation with Finn that to Prismo seems like he's just talking to an empty room. Maybe.
Ricardio: The plasmordial layer is completely independent of the Babylons. Princess Bubblegum: Wow! That would mean that the Babylons would fluctuate with the piranhananosphere! Ricardio: Correct. Finn: They're talkin' about science, man. I can't compete with that!
Jake: Seriously, the only foreseeable threat might be all these trees being swallowed, but they're not hurtin' nothin'. Finn: Yeah... Good thing [the monster's] not swallowing some deadly volcano lava. That would kill them for sure! (The monster considers this and heads for a volcano.)
The Assimilator: GOLB's monsters behave this way, attempting to absorb Candy People to strenghten their bodies. PB realizes this and orders the Banana Guards to retreat, though she didn't count on the Gumball Guardians also being susceptible to the assimilation.
The Character Died with Him: Flame Lord was noticeably absent from the lantern in "Bun Bun", most likely due to Roddy Piper's death due in July of 2015.
The Corruption: GOLB's breath can turn anything it comes in contact with into horrific monsters. It's heavily implied that the Lich was created when a bomb made from GOLB's breath exploded near a human.
The Final Temptation: Puhoy. A Tearjearker as well. It's both played straight, subverted and then played straight again.
The Three Faces of Eve: Applies to the three main female characters: PB the life-creating mother, LSP the immature child, and Marceline the free spirit.
Returned to more darkly with "All the Little People," in which Finn's obsessive shipping of animated figurines of the show's characters is portrayed as unhealthy and connected to his ongoing depression.
Those Two Guys: The two gumdrop girls. They're frequently seen in the background, almost always seen together, and have had absolutely no impact whatsoever on the plot.
Jake and Lady are typically this, but Jake has used his stretching powers on 1 or 2 occasions to be the bigger one.
Finn whenever he hangs out with Canyon, as in "Billy's Bucket List" and "Mama Said."
Title Drop: The term "Adventure Time" serves as the eponymous duo's catch phrase, lead into by Finn saying "What time is it?".
There are also permutations of it in a few episodes. "Slow Love" saw "Lady Time", "The Dungeon" featured Jake joyously proclaiming it to be "Lunch Time," and "Susan Strong" has Finn help Susan using "Incremental Time."
There are a few "episode" title drops like in "Loyalty to the King", "What Have You Done?", "The Real You", and "Go With Me".
From "Too Young":
Lemongrab: TOO YOUNG! TOO YOUNG TO RULE THE KINGDOM!
And now we have this from "Too Old", which featured several call-backs to "Too Young" (as the name suggests):
Lemongrab: YOU'RE TOO OLD PRINCESS! TOO OLD FOR PRANKS! TOOO OOOLLLDDD!
Parodied in-universe in "Heat Signature" for the movie Heat Signature. Try to figure that out.
"AAAH, MY HEAT SIGNATURE!!"
"YOU MADE ME LIKE THIS! YOU MADE ME! YOOOU MAAADE MEEE!"
"IT'S ALL YOUR FAULT! ALL YOUR FAULT!"
Simon(whispering): You forgot your floaties...
The Lich drops the title of "Wake Up" to Old Man Prismo, just before killing him.
Together in Death: Ghost Princess and Clarence fall in love while they are ghosts in "Ghost Princess". Eventually, though, the trope is played straight when it is revealed Clarence killed Warrior Princess in a war.
The penalty for stealing boots in "Ocean Of Fear" is poots on the newts.
Two episodes end with a character farting - "Slumber Party Panic!" has a character yell "Don't squeeze me, I'll fart!" and then Jake does, and in "It Came from the Nightosphere", it's revealed that Jake has been sleeping in Finn's pocket the whole time - Jake turns over and farts, and the episode ends.
In "Too Young," Finn mentions wanting to force-feed Lemongrab spicy serum "non-stop, 'till his butt falls out!" (He ends up violently throwing up instead, though.)
A hidden one in "All Your Fault" reveals one of Lemongrab's thoughts in the infamous "brain screenshot" and possibly reveals why he prefers mild, bland foods:
The Hotdog Knights. When given a chance at being granted two wishes, they wished for a box and to be blown up, respectively. Hotdog Princess is aware of this and it's why she sent Finn and Jake to help rescue them.
Finn and Jake in "Heat Signature". When Marceline clearly tells them that the ghosts will suck their guts out when they (Finn and Jake) go to the their (the ghosts') house, Finn and Jake go anyway because the ghosts say they want to "throw a party in honor of [their] new vampire skills." Meaning that Finn and Jake trust ghosts over someone they've known longer.
In "The Pods", Fin and Jake are given 3 magic beans, but are warned that one of them is evil. Their plan? Plant all 3 beans to see which one is evil, of course!
Lemongrab and his clone: They don't even pay attention to the fact that both of them- and their new subjects- are starving since they've grown obsessed in creating 'life' using the formula Bubblegum accidentally left behind. Thus, they would have died due to their impulsiveness and their obsession.
Too Long; Didn't Dub: Done for joke purposes in "My Two Favorite People." Lady Rainicorn tells Jake a joke in Korean. Jake finds it hilarious, but when Finn asks what it is, Jake says sheepishly that it "doesn't translate very well." According to the storyboards for that episode, it actually wasn't much of a joke.
Lady Rainicorn: I can't think of one... but remember that time we ran naked through that farmer's cabbage patch? He was so offended. Jake: Let's not talk about that.
Totally Radical: Everybody talks like this. The series loves coming up with deliberately goofy slang, such as "mathematical" and "algebraic". Largely justified, in that it takes place in a post-apocalyptic world, meaning that the characters' understanding of slang would be taken from the movies, video games, and other entertainment that remained after the Great Mushroom War.
Tragic Monster: Ice King and Lemongrab definitely. The Lich may also count if his implied origin ( that he was a human who was directly hit by one of the bombs from the Mushroom War) is true.
Trailers Always Lie: The preview for "Burning Low" heavily implies that Princess Bubblegum is jealous of Finn's relationship with Fire Princess. However, the truth is that she's only against their relationship because kissing Fire Princess would cause her to go unstable and destroy the world.
The trailers for the Grand Finale all but outright lie by seeming to show the Candy Kingdom and Gumbaldian armies rushing toward each other for battle. In fact, the battle never happens, and both armies are fleeing from GOLB.
In the week before "Ricardio the Heart Guy" aired, teasers for the episode on Cartoon Network all but completely spoiled that he was evil, despite how ambiguous the first half of the episode tried to make it, and also showed the part near the ending in which Ricardio had tied up Princess Bubblegum and was holding a broken bottle to her, and Jake punched him.
The commercial for "In Your Footsteps" spoiled the fact that the bear steals the Enchiridion at the end. It did NOT, however, spoil the fact that the bear gives the Enchiridion to the Lich at the end.
Averted with the long teaser for "A Glitch is a Glitch", which used clips from older episodes to essentially say "we can't show you anything from this episode because it's too crazy, so have a Regular Show clip instead."
Bizarrely enough, Cartoon Network spoiled the secret theme of a Five Short Graybles episode, "Another Five Short Graybles", by having the announcer say out loud what it is, and the secret themes are usually the entire POINT of the grayble episodes.
Traintop Battle: Finn and the creepy conductor have one in "Mystery Train".
Translator Microbes: Jake dropped a neck-worn translator device on the bottom of the lake in "My Two Favorite People." The reason he dropped it was because it only had three output voices: Nightmare, Old Man, and Alien Nerd.
Trapped in Villainy: In the episode "Jake vs. Me-Mow", Me-Mow forces Jake into killing Wildberry Princess with the threat of death.
True Love's Hug: In "Too Young", a "love-hug" from Finn is needed as a catalyst to mix the candy people's biomass with Princess Bubblegum's (to turn her eighteen again)... They still kiss just for the hell of it.
Teased in "Gumbaldia" when Gumbald gathers a legion of one-shot villains to attack the Candy Kingdom. Proves to be a "Shaggy Dog" Story when all of them just run away.
Uncanny Valley Make Up: Tree Trunks when she tries to seduce an enemy. At the end of the episode, Finn and Jake try it, and Finn looks straight-up scary.
Undeath Always Ends: The Lich was newly restored to life as a baby at the end of the season 6 premiere.
Unexpectedly Dark Episode: Adventure Time has several episodes like this, including "I Remember You", "Simon and Marcy", and "Evergreen". The first two deal with the backstory of Ice King, generally a comic relief villain, and reveal him to be a Tragic Villain with a sympathetic backstory. He used to be Betty's fiance Simon, before wearing the Ice Crown drove him insane to the point where he doesn't remember who he was. The third follows the history of Ice King's crown and has a Downer Ending.
Unexplained Accent: Flambo's Bronx accent, Tree Trunks' Texan accent, and Goliad's English accent, all contrasting with the Midwestern newscaster voices all of the other characters use. Flambo can't even use the excuse of his voice actor naturally having the accent.
The Irish accent of Finn's mother, Minerva.
The Unreveal: Is Susan Strong human or hyooman? In "Beautopia", it's revealed that she's most likely human, though it's still technically ambiguous.
Islands confirms that she is definitely a human with cybernetic implants.
Unspecified Apocalypse: The Great Mushroom war is the reason behind the formation of the Land of Ooo, but for the longest time, the end was only hinted at being some sort of war.
The fall of the Candy Kingdom as indicated by "Graybles 1000+" and "Lemonhope." We don't know what happened, or if anything even happened other than natural decay. But "Come Along With Me" demonstrates that life will go on.
Though, as is eventually shown, there really IS a Glob. But he never says "Oh my Glob." Sometimes Gob does.
Honestly there's probably too many examples to list. Probably almost as many unique examples as there are episodes. Given the show's setting, it can probably be justified as Future Slang.
Unusually Uninteresting Sight: Betty. Within seconds of being brought to Ooo she had no reaction to a teenager wearing a bear skin hat, a talking dog, or a vampire, not to mention being in a palace made of ice. There was still no reaction to using a magic carpet a minute later. All that her attention is drawn to is Simon.
Up to Eleven: Marceline's bass amp goes all the way up to XII.
The Lord of Evil's Eldritch Abomination form as well as the dimple plant's dangerous form have mouths that seem to resemble this.
The slime monster in "Dad's Dungeon".
Valentine's Day Episodes: "Incendium". The trappings of the holiday aren't present, but romance is the main theme and the fact that it was airing on "Valentine's Eve" was pointed out in advertisements.
Vampire Hickey: Marceline has two noticeable bite marks on her neck, indicating that she was turned some time in the past. The "Stakes" mini-series eventually reveals in a flashback, to when she was just a common half-demon (human mother, demon father), that this was from the vampire king who bit and turned her just as she was staking him. In the present day of the story, when she regains the last of his vampire power, the vampire essence puts the marks back on her neck as she's absorbing the power.
Villain Over for Dinner: Invoked when Finn begins unleashing his greatest fears in an attempt to escape the dream world in "King Worm": one of his fears is being too young to hang out with Princess Bubblegum, so it manifests with her having coffee with the Lich (also one of his greatest fears).
Vile Villain, Saccharine Show: The Lich is probably the best example, being a horrific, omnicidal undead monster and pretty much the only villain that isn't humorous in any way. The Fight King, Ricardio, Me-Mow, and the Freak Deer are all also a lot scarier than you would expect from a show like this.
Violence Really Is the Answer: This show just takes this trope and runs with it. A lot of times, Finn and Jake just solve something by beating or threatening to beat the crap out of it. It is even the Aesop for one episode, "His Hero".
Subverted later on, starting with "Gumbaldia" and leading into the finale. Finn has grown up a lot, and has realized that a war between PB and Gumbald will solve nothing. He's learned that violence has its role in the world, and that Billy's philosophy went too far, but it shouldn't be resorted to when there's an alternative.
The Virus: The Lumps. When a Lumpy Space person bites a normal being, the normal being turns into a Lumpy Space person. It's like,... werewolf rules? Rawr-rawr-rawr.
Played much more seriously in the "Islands" miniseries. Minerva originally digitized herself because she was dying of a plague that killed 60 percent of humans—and 99 percent of the doctors who tended to them.
Jake: It's hard to think on an empty stomach... I wish I wasn't so hungry. (sub sandwich appears and Jake takes a tiny bite) Finn: You wasted your wish, man!
Jake almost does this again in "Jake the Dog," again over a sandwich. Fortunately the genie was fairly benevolent (to him, at least) and put a stop to it, basically telling him what wish he needed to save both Finn and the pre-wish multiverse.
We Are as Mayflies: Inverted. It's heavily implied that Jake ages in dog years and will reach old age while Finn's barely into adulthood.
We Want Our Jerk Back: Donny has to go back to being a jerk so he can repel the whywolves with obnoxygen, thus saving the house people. Oddly, no one directly involved wants him back. The house people, whom he inadvertently protects, don't like him, and the whywolves seem very enthusiastic to hunt the house people to extinction even knowing that they'll die afterward.
Whywolf: ...until we, in turn, are devoured by the Cosmic Owl. Such is the nature of things. But! It'll be a pretty sweet ride up until that point.
From "Candy Streets", Pete Sassafras is still locked up in Candy Kingdom jail, even though he was totally innocent.
In "Crossover", the Lich's severed, still alive hand is multiplied and sent to every dimension in the multiverse. While the copy in the main universe is destroyed in "Whispers", what happened to those in the other timelines?
There are a lot of these in "Daddy's Little Monster".
White-and-Grey Morality: While there can be straight up evil characters, at least 90% of the villains have backstories and depth that makes them seem more human. With the addition of the Lich, the series overall morality is The Good, the Bad, and the Evil with Finn and Jake as heroes, the Lich as the Big Bad, and everyone else with flaws and redeeming qualities.
Like everything else, the show complicates this as it goes on. Finn is shown to have serious flaws in his ideas of heroism and romance that he needs to work through. Jake is a lot more put-together, but has still made plenty of mistakes. Furthermore, plenty of villains are introduced who are just jerks, even though they have perfectly good reasons to act that way. Ultimately, the series seems to be saying that traditional moral axes just doesn't match the real world.
Fionna throws an ax in the Fionna & Cake story Marceline tells in "Bad Little Boy" to cut an apple balanced on BMO's head in half
In "Holly Jolly Secrets", the Ice King attempts to use his ice powers to shoot an apple off Gunther's head and ends up encasing Gunther's head in ice.
Wishing for More Wishes: In "The Limit," Finn and Jake and a group of hot dog knights quest through a labyrinth, at the center of which is a being that will grant each of them one wish. Finn and Jake have decided to wish for an Ancient Psychic Tandem War Elephant, but by the time they get to the center of the labyrinth, several of the hot dog knights have fallen and Jake is near-death from over-stretching. The hot dog knightswaste their wishes on frivolous and poorly-considered things rather than restoring their fallen comrades, and Jake accidentally wishes he weren't so hungry and is granted a Satiating Sandwich, leaving only Finn's wish. The moment is played as a choice between a selfish wish for the APTWE or a selfless one for Jake to be healed, and Finn seems poised to go with the latter... until he wishes for the APTWE, psychically proves his worthiness to become its master, and orders it to wish for Jake and the fallen hot dog knights to be restored and then fly them all to safety.
Witch Species: Played straight or Gender Flipped, as Word of God gives "Wizard" as the species for Ash and the Ice King (though the latter was born human). We also see "witches," but it's unclear if they and Wizards are the same species, two examples of this trope or what.
Huntress Wizard raises further questions, though she may be some sort of nymph.
The speech at the end of "The Other Tarts" seems to be complete nonsense:
Royal Tart Toter: This cosmic dance of bursting decadence and withheld permissions twists all our arms collectively, but if sweetness can winand it canthen I'll still be here tomorrow to high-five you yesterday, my friend. Peace.
Anything Cuber says. Ever.
The Worf Effect: In "Blade of Grass", Finn is Cursed With Awesome by obtaining a cursed sword that, like cursed weapons from RPGs, cannot be un-equipped. Its magic appears to also give some sort of RPG-like "dexterity stat bonus" that makes Finn far, far more awesome at using it than he would otherwise be, showing him carving a picture of his face into objects with a flick of the wrist. In the very next episode "Rattleballs" however, to emphasize how much better a swordsman Rattleballs is than Finn, this effect seems to completely disappear, to the point that not only does Finn not stand a chance against him in a swordfight, but finds it challenging simply to deflect eggs thrown at him in a training excercise.
"Tree Trunks" opens in Tree Trunks's apple orchard, where Finn and Jake are chopping up apples with their swords. A green worm eagerly approaches one of the apples, only for it to be halved right before the critter reaches its intended meal.
In "The Real You", Finn and Jake attend the Worm College. Worm College is located in a giant rotten apple. It doesn't last long because the fingers of the duo are mistaken for truants and attacked by the worm-students.
Worthy Opponent: Jake and Finn enjoy fighting "Science Cat and Sword Shark" for recreational purposes in My Two Favorite People.
Writer on Board: Jake's whole conflict with eating Meat Man in "Hitman" could be interpreted as a message to the viewer that they should question eating meat. One of the episode's storyboarders was Jesse Moynihan, who is a vegetarian.
Also Princess Bubblegum being aged back to 18 in "Too Young," right when it seemed that her and Finn would finally become more than friends.
Her pushing Finn further away in "Incendium".
Just when Finn starts to finally quell Flame Princess's emotions for good so that they can be together, she realizes that Finn secretes water through tears when they hug, so they can't be a couple. That is until a later episode, but there are still obstacles.
Year Inside, Hour Outside: In Puhoy this happens to Finn. He goes to a pillow world, grows up, gets married, and has children. After he dies, he wakes up again in his own world a few minutes after he left, and begins to tell Jake about a crazy dream he had. A phone call interrupts him, and Finn totally forgets even having a dream...if that's what it was in the first place.
Yet Another Christmas Carol: The picture book "A Christmas-tastic Carol" places Ice King in the role of Scrooge, Marceline as Christmas Past, Lumpy Space Princess as Christmas Present, and Finn and Jake as Christmas Future.
You All Meet in a Cell: The episodes "Return to the Nightosphere" and "Mystery Dungeon" both begin this way. In the first it's Finn and Jake waking up in a cage in the Nightosphere. In the second, it's Ice King and several minor characters in a dungeon.
Then regained it in "Breezy," lost it again in "Reboot," got a mechanical replacement in "Two Swords," then lost that in "Come Along With Me." The fact that he doesn't have another prosthetic the final time he's seen in the show probably means that he's given up bothering and accepted the universe doesn't want him to have a right arm.
You've gotta wonder how much longer poor Shermy has with his right arm.
The businessmen's weird grammar in "Business Time."
"We love work for you!"
Susan Strong's English in general.
"Susan have hero's heart!"
Explained in Islands—she's a full-blooded human with cyborg implants from a post-apocalyptic refuge, who arrived on Ooo to recover the infant Finn but got damaged somehow and never completed her mission.
Gunter lays an egg in one episode. The characters even lampshade it. That said, the exact details are fairly ambiguous. After all, a magic cat creature hatched from the egg.
Also: The Ice King apparently lacks the capacity to differentiate between one penguin and the next, so they're all Gunter, further complicating the issue. When attempting to determine the gender of this particular Gunter, he tries looking at the penguin's general crotchular area, which doesn't do him much good (look up "cloaca" sometime).