Adventure Time is a mostly episodic show, but there are moments that remind you that there is a story going on.
During "In Your Footsteps", at the end of the episode, we see the Snail being possessed by The Lich like in "Mortal Folly", who planned to steal The Enchiridion for unknown reasons.
In "Beyond this Earthly Realm", when Finn is looking for the Ice King, he says "Where'd you go Simon?" This is referring to the Ice King's real name from when he was a human, as learned in "Holly Jolly Secrets Part II."
The beginning of "Sneeze the Day" is a call back to the scene where Aladdin steals a loaf of bread in the original film. In the episode, Amin Damoola steals a diamond and Aladdin, Genie, and the royal guards try to stop him from escaping. The scene depicts the same dialogue used in the scene of the movie.
Heads, You Lose: Moments after Aladdin gets his head removed from his body by Caliph Kapok, Aladdin's body spins his head and juggles it, with Genie commenting "Taught him that trick the first time we met."
Shadow of a Doubt: Aladdin and his friends (save Genie) enter a cave where they have to find a mirror that represents "the truth behind appearances." After Aladdin finds the mirror, Iago attempts to steal a mirror that shows a reflection of himself wearing gold and jewels, causing the cave to collapse. This scene is very similar to the Cave of Wonders scene in the movie. Hell, Iago even mentions the Cave of Wonders incident when he tells Aladdin not to let Abu touch anything.
American Dad!, of all shows, has a surprising amount of call backs. Unlike other animated comedies, the writers seem to be putting a surprising amount of effort into keeping continuity.
One episode shows Stan sending a realtor/hand model to Guantanamo Bay. When she borrows another inmate's napkin, they say they will cut off her "beautiful hands". Later episodes show her with a hook for a hand, and at one point was even introduced as a "former hand model".
Another episode features a subplot involving a cat that constantly attacks Steve. The end of a later episode shows the cat using a gun to kill Steve's clone.
In Season 1, Stan sends a bitter, wigless woman to the CIA and claims she is the alien they were looking for. Five seasons later, Stan and Roger go to Area 51, where the old woman can be seen in a tube full of green goo in the background.
An early episode has Francine mentioning George Clooney as her "one free kill". A later episode reveals that she really hates him for stealing her chance at fame, and she spends the entire episode trying to make him suffer by breaking his heart.
In Season 1, Stan casually mentions having a half-brother. Guess which member of his family we meet much later on?
Archer's main source of humour is the callback, a carryover from Adam Reed's previous project Frisky Dingo.
As Told by Ginger was actually well known for this. In every single episode, except the first, they make some form of reference to a previous episode, and everything is kept in continuity.
There's a fun little Call Back involving turtleducks: In a flashbackZuko shows his mother "How Azula feeds turtleducks" by throwing a loaf at them. In the present, while Zuko is feeding the turtleducks they suddenly scatter... Because Azula shows up.
In "The Western Air Temple", the Gaang reminds Zuko and each other of all the bad things he did to them in the first season. They continue to reference them throughout the rest of the season.
In the same episode, Zuko accidentally burns Toph's feet. After Combustion Man is killed and Zuko apologizes to Toph, Aang remembers that he himself accidentally burned Katara (In "The Deserter"). Knowing full well how destructive uncontrolled fire can be to the ones you love, Aang accepted Zuko as his Firebending teacher.
During Zuko's lightning redirection training, Iroh warned him to guide the lightning through the stomach, and never through the heart. In Sozin's Comet, Part 3, Azula throws lightning at Katara. Zuko jumps in front of Katara and attempts to redirect the lightning, but in his panic, he guides it through his heart. He ends up on the ground in the fetal position, barely conscious, twitching and groaning as residual lightning sparks through his body. He's quickly healed by Katara, but he still wears bandages and needs help dressing himself weeks after the battle. Listen to Iroh, everyone.
In one episode of Camp Lazlo, most of the campers show Raj and Samson that they came down with a mystery rash, which, according to Samson, Edward still has in a later episode. In that one, Edward drives his cabin like a car, which becomes a plot point a few episodes later.
Clerks: The Animated Series repeatedly references a scene from the first episode where Dante and Randall appear to be climbing a building, only to pull back and reveal that they're simply doing a Bat-Climb.
There are a few call-backs in Danny Phantom, but one of the most blatant is in "Memory Blank" when Danny lists events that happened in previous episodes to use against Sam during a bitter argument.
Like the name implies, "Dee Dee's Rival" at least starts out as a scene-for-scene remake of "Dexter's Rival," appropriate considering the latter introduced the show's default Big Bad Mandark and the former introduces his sister.
In addition to his Giant Robot, the Giant Dexo-Robo, showing up prominently in several episodes, his power frame (first called the "Dextransformer" then later the "Exerjock 4000") from the early first season dodgeball episode reappears in three late Season 2 episodes, the first one ("Gooey Aliens That Control Your Mind") specifically mentioning the "dodgeball incident" (and including a sweep pan over a room of previous episodes' inventions).
Dexter brings back his "Dex-Star" identity from "Sidekicks Assemble" to fight alongside Blue Falcon and Dynomutt.
A meta-example in that the second act of "Last But Not Beast" features Monkey and the Justice Friends fighting the kaiju, just as they were the second cartoon short in the first season.
In part 2 of the 5-part "Super DuckTales" story on DuckTales (1987), when Fenton first accidentally gets the Gizmo Duck suit, he shouts out "I'm being canned like a tuna!" In a much later episode, "A Case of Mistaken Secret Identity," when Launchpad is trapped in the Gizmo Duck suit, he describes himself as "feeling like a canned tuna." Coincidence? I think not!
In the Ed, Edd n Eddy episode "No Speak Da Ed", after Rolf kidnaps Ed because he believes him to be in league with the wolf who tormented his livestock as a child, Eddy is unconvinced that Rolf will do anything serious to the Eds and suggests that he'll stick eels down their pants again like he did at the end of "Dueling Eds".
In the second episode of Exo Squad, police officer and future Resistance leader Sean Napier saves Phaeton from an assassination attempt. Later on, he refuses to shake Phaeton's hand because "Saving his life was my job. That doesn't mean I've forgotten what you Sapes did fifty years ago." Phaeton doesn't take it very well. In the final episode, Napier, who has become a politician since the end of the war, is giving a speech about the need for reconciliation and cooperation to some Neosapien POWs. One of them pulls a gun and tries to kill him, but he is saved by General Shiva. When Napier tries to shake Shiva's hand, he refuses, explaining that "the past cannot be forgotten". But, he adds, if Napier meant what he said before, "someday, I will be glad I saved your life."
Yet another good example: In "To Love and Die in Dixie", Peter has decorated the family car like the General Lee, but when Brian's attempt to jump into the car Duke-style is thwarted because Peter forgot to roll the window down. Jump ahead to "The Fat Guy Strangler" where Brian throws a rock at Peter's head, telling him it was payback for the previous incident.
Another example is when Peter becomes a redneck and he starts chewing tobacco. Brian tells him to spit in a cup. Later, Stewie comes along and takes the cup and is about to drink it because he mistook it for his cup of apple juice. Brian starts to warn him, but flashes back to the episode "Patriot Games" (where Stewie horribly beat Brian for not immediately paying a gambling debt) and changes his mind, letting Stewie drink it.
The same episode (from Season 5) would set one of the longest Call Backs in the series; Peter, talking like a redneck exclaims "Oh, that dog of mine!" In "Brian's a Bad Father" from Season 12, Stewie says the same sentence and lampshades it, followed by a jingle: "Family Guy, we've been on for years!"
Likewise, Peter's attempt to integrate into Southern "good old boy" culture in "Boys Do Cry" is derailed when he reveals that he is legally retarded, which was a major plot point in "Petarded."
Brian's novel is a particularly long-running example. He mentioned writing one in the early seasons; after the show was revived, there was a brief Running Gag of Stewie mocking him for not having gotten any work done in three years. Later we hear excerpts from the novel, which the family mocks for being a Cliché Storm; later still it's finally published and is a total flop, owing to being a cheap ripoff of the Iron Eagle series. The final twist of the knife comes when Brian learns that the only people who enjoy his book are mentally retarded.
"Tales of a Third Grade Nothing" in which Peter blows up a children's hospital and ends up losing his promotion when he is found guilty for his crime.
Two throwaway gags in "Jerome is the New Black" would later be relevant in later episodes:
Quagmire telling Brian that Cheryl Tiegs was the only woman he truly loved and that his sex addiction was the result of her leaving him: "Tiegs for Two" would be about Cheryl Tiegs coming back to Quagmire (but not before dating Brian). In fact, the revelation that Quagmire's sex addiction stems from a long-lost love is a callback in itself. Watch the episodes "Barely Legal," "Emission Impossible," and "The Perfect Castaway" and you will see clues about Quagmire's obsession with Cheryl Tiegs (the Missing Piece book he reads when he feels that he's missing the one thing to make him whole, the poster of Cheryl Tiegs on his refrigerator, and his reason why being blind is better than being a midget: "Every woman I did would be Cheryl Tiegs.")
The appearance of Quagmire's sister and her abusive boyfriend: on "Jerome is the New Black," it was funny in a sick way (since Brian thought that Quagmire's sister was one of his dates who liked her sex on the rough side), but on "Screams of Silence: The Brenda Q. Story," the abuse and everyone's reaction to it would be more on par with what you would find on a Very Special Episode of a sitcom.
In "Life of Brian", after Brian's death, the Griffins are looking for a new dog. Stewie tells Chris that he's kind of a creep and that he should get a ferret, and Chris agrees to both. Later, Stewie tells Vinny bad news about various Italian people he knows in an attempt to send Vinny into cardiac arrest and almost succeeds until Chris come in and tells him that one guy's son beat his cancer. When Stewie asks Chris what is he doing, Chris yells "Call me a creep, you piece of crap!" and punches him out.
In the same episode, Peter tries to signal a plane for help with a flare gun and accidentally shoots it down, killing the pilot. At the end, Peter nonchalantly mentions getting to kill a guy, much to the retreat director's horror.
The plot of Fry being his own grandfather as a result of "Doing the nasty in the past-y," later becomes an explicit plot point.
Amusingly blatant example in The Garfield Show. When asked why he's so concerned about a bluebird, Garfield flat-out says "Don't you remember the episode last season when I rescued the baby bluebirds?"
When Demona's plan to betray the humans of her castle so that the gargoyles would have it to themselves went wrong and resulted in the deaths of most of her clan and the rest being frozen as stone for good, she says "What have I... what have they done?!!" At the very end of the show, John, a human hunting gargoyles, accidentally shoots his brother while attempting to shoot Goliath, and says the exact same words.
"Hunter's Moon" is full of Call Backs to previous episodes, especially in "Awakening" and "City of Stone." For example, in the very beginning of "Awakening", Elisa is investigating the battle on top of the Eyrie Building and comes across a stone with claw marks in it, to which she muses, "What could be strong enough to leave claw marks in solid stone?" Then, in "Hunter's Moon," Elisa and her partner are investigating a crime scene in which a gargoyle tore a steel door off of its hinges, and Elisa's partner asked "What could be strong enough to leave claw marks in solid steel?"
In "The Edge" Owen mentions a meeting with an Emir to Xanatos. Later, in "Grief" the Emir is actually a character.
Goliath occasionally mentions "needing a detective." In the first episode, "detective" was the first new word that Goliath learned after waking up in the 20th century, and he advised Xanatos to "call a detective" to find his lost disks soon after learning it.
A surprising number of Fillmore! episodes feature background appearances by characters from previous episodes — the science fair in "The Shreds Fell like Snowflakes" has blink-and-you'll-miss-it appearances by one of the would-be perps in "A Cold Day At X" and the psychic from "Cry the Beloved Mascot".
In the episode of Goof Troop "Axed By Addition", Pete says that one time he made PJ pluck dog hair out of the carpet with tweezers. Evidently, it was more than once since the task is referenced as something PJ needs to do in both "Take Me Out of the Ball Game" and "And Baby Makes Three."
A disturbing one occurs in Gravity Falls. In "Into the Bunker", as the shapeshifting monster is being frozen, he taunts Dipper by morphing into an image of him horrifically screaming, saying it will be "the last form [he'll] ever take". In "Northwest Mansion Mystery", Dipper is turned into a wooden statue whilst screaming in a very similar pose (though since he's turned back at the end, the monster's prediction wasn't exactly correct).
There's also a much sweeter one: in the premiere episode "Tourist Trapped," Dipper offers Mabel an "awkward sibling hug" once the two make up after an argument. Then in the penultimate episode "Weirdmageddon 2: Escape From Reality," Dipper offers Mabel an "awkward sibling hug" again, after a much more serious fight, only for her to counter with a "sincere sibling hug."
That kryptonite Batman carries around? That came into play when fighting Amazo? He got it twenty episodes earlier, in "Injustice for All", when fighting Luthor, who, at the time, was armed with kryptonite. Green Lantern took it from Luthor with his ring, but Batman grabbed it from midair and put it in his utility belt, where it stayed for almost a full season.
It gets better. Amazo blasts the kryptonite into splinters, leaving only a single useful piece. This piece is the one Bruce gives to Terry McGinnis in the Batman Beyond two-parter "The Call". Since Batman Beyond was made before Justice League, in reality, it's a Call-Forward.
Ninjago has a habit of introducing new plot elements that are intentionally left unresolved so that the story can revisit it at a later time. For example, the Mega Weapon is blasted into space near the end of the episode "Wrong Time, Wrong Place" to prevent Lord Garmadon from altering the present. Fast forward one season later, and the ninja find out in the episode "Codename: Arcturus" that the Mega Weapon landed on a comet and that Pythor intends to retrieve it in order to return the Overlord to power. Cue Space Episode.
The Powerpuff Girls episode "Reeking Havoc": Buttercup asks Blossom where she got a giant match to battle a giant fart monster.
Blossom: Same place I got the giant jar from, silly. Season 1, Episode 2... remember?
In "Keen on Keane", the Professor recalls a bad experience with a cat that made him "jump off a building", a nod to the episode "Cat Man Do".
In "Aspirations," Bubbles mentions Buttercup's crush on Ace of the Gangreen Gang from the episode "Buttercrush."
Buttercup: Why you gotta bring up old stuff?
In The Problem Solverz episode "Magic Clock", the Eternitron from "Time Twister" can be seen in the background of the clock museum. Also, Fauxboro, from the previous episode, is the setting for Roba and Katrina's wedding.
The Ready Jet Go! episode "The Grandest Canyon" references an earlier episode where Mindy mishears "perspective" as "respective", only this time Mindy can say it and it's her friend Lillian who has the same trouble with the word. Mindy lampshades the situation.
In "Mars Rock for Mom", a reference to the end of "Try and Try Again" is made, and is a crucial plot point. In that episode, the kids want Jet 2 to be their Mars rover, so they give him a new set of wheels and take him to Mars. However, Jet left Jet 2 there. During the time in which he was stranded there, he has adapted to the Mars environment and apparently formed a relationship with Boop.
In the "Who Shot Mr. Burns?" two-parter, Smithers' throwaway comment in part one about never missing the Comedy Central show Pardon My Zinger (which isn't a real Comedy Central show) ended up providing his alibi for not having shot Mr. Burns in part two.
In "Treehouse of Horror XIV"'s first segment "Reaper Madness", Homer becomes the Grim Reaper after accidentally killing the original. In the following segment "Frinkenstein", as Frink Sr. goes on a rampage at an award ceremony, he declares "I wish I was Death again. That was cool."
The Gainax Ending to Season 16 episode "Butterballs" is referenced at the end of same season's "I Should Have Never Gone Ziplining". Both occur when Stan achieves fame for raising awareness for a certain problem (bullying in the former, the literally lethal boredom of ziplining in the latter).
In the first Halloween episode, Wendy wins the school costume contest with a Chewbacca mask. In the third, Kenny enters the contest with an insanely elaborate Humongous Mecha costume and seems a shoo-in to win... only for Wendy to win again with the exact same mask. They might even have relooped Mr. Garrison's announcing her winner for that one.
In the Season 3 episode "Starvin' Marvin' in Space", Cartman blames Kyle for a turd in the urinal. Season 10 makes an episode note out of finding out who took a crap in the urinal. Cartman blames Kyle, obviously. After a purposefully convoluted plot, it turns out to have been Stan.
In the Season 8 episode "AWESOM-O", a disguised Eric Cartman asks Butters to reveal private aspects of his life. After mentioning a particularly embarrassing bowel condition, he mentions a bully namedyou guessed itEric Cartman who likes to play tricks on him. The two incidents he names are from previous episodes: "Jared Has Aides" and "Casa Bonita".
In the theatrical movie, General Plymkin shoots Bill Gates in the head after what he believes is a glitch in Windows '98. Gates later appears in "The Entity" (airing two years after the film was released), only this time, with a band-aid poorly covering a hole in his head.
In "Elementary School Musical", the boys are asked rhetorically "Where have you been?" when they say they don't know anything about High School Musical. Craig replies "Peru", a callback to "Pandemic" earlier in the season.
In "The Coon", Cartman holds a failed rally for his eponymous superhero alter-ego, where the attendant asks him if he's the same kid that held the "Ginger Pride" rally from "Ginger Kids" and the AIDS benefit from "Tonsil Trouble," which Cartman angrily denies.
In an early episode of The Spectacular Spider-Man, Spidey saves a geeky guy and a hot girl and in his rush webs them up together and hollers "You can thank me later!" to the guy who is now making eyes at the girl. Later in the latter part of the second season, the geeky guy is proposing to her.
One episode had Man Ray use role-playing to become good. SpongeBob first tries to teach him good by giving back someone a wallet they dropped. Man Ray does this to Patrick, but is so dumb he doesn't even think it's his wallet despite his ID being in it. SpongeBob's second lesson is for Man Ray to help someone carry a heavy package. Patrick keeps dropping the heavy package on Man Ray's foot. He gets furious and asks what is even in the box to which Patrick replies, "My wallets". That one's more of a Brick Joke, really.
Another episode had Bikini Bottom terrorized by sea whelks. When everyone is trapped inside, SpongeBob remembers the time he had the suds in the first season episode "Suds", which he uses to free everyone and return the whelks to normal.
Steven heals Lapis Lazuli's gemstone in the episode "Ocean Gem". He tells her "No prob, Bob" after she thanks him. Taking his reply literally, this prompts her to tell Steven that her name is Lapis, not Bob. Fast forward to the episode "Hit the Diamond" and Lapis uses the name "Bob" as an alias for her masterfullyhuman disguise to fool a team of Rubies from Homeworld.
In "Marble Madness", Steven rambles off a brief list of Beach City's citizens when Peridot inquired whether Earth still has humans. This list pulls a Chekhov's Boomerang at the end of Season 4, when Aquamarine reveals the reason she and the Topazes are on Earth kidnapping people is that they're collecting the listed "types" of humans.
Though Superjail! is mostly episodic and prone to the reset button, the cliffhanger in Season 2's finale is revisited in the Season 3 premiere, after a short time skip. The inmates become aggravated with the current state of the integrated "Ultrajail", and think back to what happened after they were captured by the Mistress.
In Teen Titans "Aftershock: Part 1", two mentions are made of the "Apprentice" episodes from Season 1 (not surprisingly, given the parallels between the two episodes).
Timon & Pumbaa has several call backs to the original film. Some episodes also have call backs to some previous episodes.
"Kenya Be My Friend?": When Timon and Baampu are stargazing, Baampu asks Timon what the sparkling dots in the sky are, which Timon replies that they are fireflies. After a moment of silence, Timon asks Baampu if he's going to state that he always thought they were balls of gas burning billions of miles away, which the warthog replies that he will not, much to Timon's depression, making him start to miss Pumbaa.
"Home Is Where the Hog Is": When Pumbaa reunites with his sounder, Timon interrupts Pumbaa and Sharla's moment and says "Let me get this straight. You know her, she knows you, they know you. What's going on here?!"
"Gabon With The Wind": When Cheetata calls Pumbaa a pig, Pumbaa goes berserk and charges at the cheetahs, with him and Timon using the same dialogue used in the movie when he goes berserk and charges at the hyenas when Banzai calls him a pig.
"Zazu's Off-By-One Day": When Zazu runs into Rafiki, he asks the baboon if he knows which animal he forgot to count. Rafiki shows Zazu his reflection in the water, though when he tries to do so on the first pool, he ends up showing Zazu a reflection of Simba instead of the hornbill himself.
All of the Speedy the Snail episodes end with Timon and Pumbaa saying goodbye to Speedy when they take him home, only for Speedy to get caught by a seagull and Timon and Pumbaa having to save their friend once again. In Speedy's final appearance, the seagull turns out to be an aircraft controlled by Chromosome Quint.
In the Yukon episode, Tyler complains about being ignored by everyone, mentioning that Lindsay even called him "Noah" earlier. The next episode opens up with Team CIRRRRH not noticing Noah was missing all night, to which an injured Noah snaps, "Who am I, Tyler?"
Also in the Yukon, Chris says that he ordered jackets for the contestants to keep them from freezing in the icy climate, but then adds that they wouldn't arrive for a few weeks. Several weeks/episodes later, the contestants arrive in snowy Sweden, and Heather asks Chris if the jackets had arrived yet. They hadn't.
Another example is in the Season 1 finale The Monarch casually mentions to his henchmen to send Wonderboy's remains back to Captain Sunshine, this becomes a major part of the episode "Handsome Ransome" 3 seasons later.