Sacred Scripture: The hero's handbook, The Enchiridion, a legendary book that tells you how to be a hero, is not called "sacred", but it's treated as so important it might as well be.
Sadistic Choice: The guardian of the wishes in "The Limit" tried to force Finn to make one of these and choose between saving Jake and the psychic tandem war elephant he and Jake went through the maze to get. Finn wished for the elephant, got control of it and then had it wish to save Jake and fly them out.
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.
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.
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.
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!
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 friendzone him in "Earth & Water". In "The Red Throne", she reiterates that because of his "betrayal", Flame Princess no longer loves Finn in any way, and continues to friendzone him. 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".
Word Of God sank the Flame Princess x Cinnamon Bun ship, stating their relationship was strictly platonic. Good thing, too, otherwise there would be much Squick.
The entire plot of "Go With Me", up until the Ship Sinking by Marceline mentioned above. Note that relationships with both Bubblegum and Marceline were teased throughout the episode, only to be put down... until "Mortal Folly" and "Mortal Recoil" in which the amount of teasing for Finn and Bubblegum's relationship skyrocketed.
The entirety of "Too Young" was one huge tease for Finn x Bubblegum, even the title card, until the ending.
"What Was Missing" had a lot of this for Bubblegum x Marceline, and at the same time, more for Finn x Bubblegum.
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!!
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.
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.
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.
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.
Multiple guest stars have actually appeared on Adventure Time but it seems only NPH's appearance was publicized. Other people that appeared on the show were Grey DeLisle as the Ice Queen, Lou Ferrigno as Billy, Mark Hamill as The Manifestation of Fear/Fear Feaster and the Dark Magician in "The Enchiridion!", Andy Milonakis as NEPTR, Martin Olson as the father to her daughter's role of Marceline, Ron Perlman as The Lich, Henry Rollins as Bob Rainicorn, Andy Samberg as Party Pat, Laura Silverman as Ethel Rainicorn, Kumail Nanjiani as Prismo, and George Takei as Ricardio.
"Weird Al" Yankovic as the Banana Man in "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.
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 in order 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.
Usually averted: since the show takes place After the End, it would make sense for no one to really know how to properly play instruments, but some characters are decent musicians (Ice King, Jake, Marceline...)
Parts of "Adventure Time With Fionna and Cake" are written like a Fan Fic. Because it is.
The show as a whole, actually! 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.
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."
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.
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.
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!
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 Final Temptation: Puhoy. A Tearjearker as well. It's both played straight, subverted and then played straight again.
Jake and Lady are typically this, but Jake has used his stretching powers on 1 or 2 occasions to be the bigger one.
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 a number of 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!"
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.
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.
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 has recently 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.
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.
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 Unreveal: Is Susan Strong human or hyooman? In "Beautopia", it's revealed that she's most likely human, though it's still technically ambiguous.
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.
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".
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.
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 afterwards.
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.
Finn: I love zanoits! They're the best! Princess Bubblegum: Zanoits kill hundreds of thousands of plantoids a year. Finn: Oh, no, not the plantoids! Princess Bubblegum: Plantoids produce mellotoxin. Finn:(beat) Princess Bubblegum: MELLOTOXIN KILLS ZANOITS!
Fiona is doing this in the Fiona & Cake story Marceline tells in "Bad Little Boy"; using a throwing axe 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.
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.
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 win—and it can—then 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.
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.
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).
Yo Yo Plot Point: Finn bouncing between his love for Princess Bubblegum, and Flame Princess.