Fandom-Specific Plot

Fanfic is rife with tropes and Memetic Mutation. Some plots are so embedded in the collective consciousness of netizens everywhere that no fandom is complete without them, despite general disdain for them -- M Preg, for example, or Gender Bender—or even their relevance to the source material, e.g. Aliens Made Them Do It.

This trope comes in two general flavours:
 * One: Universal plots that are unusually popular within a particular fandom or pairing, for whatever reason.
 * Two: Plots which only work within a particular fandom or pairing and are incredibly common there.

As with everything to do with fanfiction, Sturgeon's Law applies.

Sailor Earth and The Ships Motor are subtropes. Compare Common Crossover.

Anime & Manga

 * In Princess Tutu, if you are a fanfic writer, odds are that you have written a story where Fakir makes Ahiru a girl.
 * Princess Tutu ends on a bittersweet note, with Ahiru . Lots of fans were unhappy with that, and that means 90% of fanfiction out there for the series is . No exaggerating. Almost. Every. Single. Fic.
 * Ranma ½ fanfic is heavy on the Gender Bender (other than of course Ranma himself) fanfics, as there's a canon way to do it. And while girl-Ranma getting pregnant isn't exactly Mister Seahorse, some fics will have him discover that yes, the pregnancy doesn't go away when he's male. (Most Pregnant!Ranma fanfics have him being trapped in female form instead.) And there's also a canon source for plenty of Animorphism fics.
 * Another common plot is Ranma discovering that he is (or is becoming) gender dysphoric, his self-image shifting to that of a girl instead of a guy, or at least a "both/neither" state. Ranma getting stuck as a girl is the usual plot device to reach this conclusion.
 * Also, Ranma ½/Sailor Moon crossovers where Ranma turns out to be a sailor senshi are so prevalent that they have their own trope.
 * "Split-Ranma" fics, wherein Ranma's male and female halves are separated into distinct individuals, but both with the same mind as the original and both locked permanently into their respective genders, were a dime a dozen in the late '90s. Some would explore the female Ranma's psychological anxieties; others would happily assume that she would gladly accept this situation and go off from there.
 * For a while during the late 1990s and early 2000s, there was a spate of "what if someone else raised Ranma" stories, with everyone from Elminster of the Forgotten Realms to Bugs Bunny taking Ranma off Genma's hands as a youngster and arriving with him, somewhat... differently trained, on the Tendos' doorstep years later. Many of these were loosely connected to the greater continuity of The Bet-verse, and came from the minicommunity of fic writers around Gregg "Metroanime" Sharp.
 * This last one is not specific to Ranma; several characters have been subject to this: Naruto, Shirou Emiya, Harry Potter, Shinji Ikari—basically anyone who had a messed up childhood that was still vague enough for some canon or crossover character to take notice and bring the kid under her/his/its/their wing. For example, Shinji and Warhammer 40 K is basically "Shinji Ikari as raised by Warhammer 40,000".
 * Then there were the "Passion Spice" fics. Based on an influential early fic, these all adhered to the fanon that among Cologne's assorted magical doodads was a collection of magical spices and herbs with various psychoactive properties—and the king of them all was the aphrodisiac "Passion Spice". Depending on the author these could range from simple farce to Plot What Plot Lemons.
 * There is an entire Fullmetal Alchemist fan community devoted to M Preg.
 * Inuyasha has a great amount of hurt/comfort with Rin as the sick person.
 * It's still a common belief that Fushigi Yuugi: Eikoden was a subtle Take That against the sheer amount of "Mary Sue is sucked into the book and becomes the new priestess" fics in the fandom.
 * Most of the fanfiction for One Piece seem to have the same few plots over and over again:
 * A retelling of the canon story, but with a new OC added. Typically will follow The Stations of the Canon almost to a T and peter out sometime before the Alabasta arc.
 * A new generation of pirates story set X years after the death of Luffy, the 2nd Pirate King. Typically will solicit readers to submit their OCs to fill up positions on the crew and as rivals/enemies.
 * An OC from the real world gets pulled into the One Piece world and makes friends with the Straw Hats, Whitebeard or the Heart Pirates. Typically later falls in love with Luffy/Zoro, Ace, or Trafalgar Law.
 * Sanji/Luffy/Nami getting sick and Zoro taking care of him/her. Instead of, you know, the actual doctor, Chopper. And yes, it always seems to be Zoro.
 * It probably has a lot to do with Zoro's position as the "eldest brother" amongst the True Companions.
 * Naruto has tons of Peggy Sue fics.
 * A lot of fics in which the genin teams are different, either because someone else is teaching Team 8 or someone else wanted Naruto, which shuffled the teams around. (These fics are most often Naruto/Hinata)
 * The infamous Clan Restoration Act, where one male character is forced to pair with multiple women to revive his clan.
 * Also there multiple fics when Naruto gains an awesome power and virtually every girl except Sakura, usually fall for him that includes his mother, Tsunade and girls he never met like Yugito.
 * Nearly every story starts with Naruto being hated and attacked by the citizens of Konoha and the Third doing absolutely nothing about it.
 * Also there are many fics that deal with Naruto bringing back Sasuke only to be betrayed by Sakura and is later exiled/executed.
 * Twelve-plus young characters of the same age, with a variety of personalities? Let's put them in high school!
 * Another really common one is the non-massacre AU, usually used as an excuse to pair Itachi and Sakura up.
 * The future arc means that the Katekyo Hitman Reborn Kink Meme is filled with age specific pairing fics such as TYL!(10 Years Later)Xanxus with 14!Squalo. Kinda justified with the Adults!Acrobalenos if you want to avoid the Squick.
 * In Love Hina fandom it's not unusual to find a fic in which Su permanently changes into her older form to become a viable love interest for Keitaro.
 * In Neon Genesis Evangelion fanfiction the Peggy Sue fic is extremely common, the most well-known being the doujin RE-TAKE (which, in a suitably Eva way, is actually ). There are fics out there that set up a For Want of a Nail situation, and then reveal that either the changes were actually caused by a Peggy Sue, or that the events of the original series had happened before. There are also Crossover fanfics where this happens. It's reached the point where some fans think that Rebuild of Evangelion is one of these!
 * Post-Third Impact fic. This can range from Shinji and Asuka by themselves in a wasteland, to everyone coming Back From the Dead and the world returned to (mostly) normal. Most of the time, Rei has vanished and Toji gets his leg back (both of which might be supported by canon).
 * Tengen Toppa Gurren Lagann Fix Fic in which aren't dead is incredibly common. Justifications tend to be that the series is based on punching physics in the face via sheer manliness anyway, so why not?
 * Zero no Tsukaima's basic premise, summoning a familiar from elsewhere, allows for almost anything to replace Saito in a crossover. The Hill of Swords has given the phenomenon some new life, but time will tell how long the trend will last.
 * In the Shugo Chara fandom, a LOT of fan fics are "Ikuto is the school playboy and has kissed every girl in the school, until the new girl Amu arrives and resists his romantic advances, will they fall in love or not?" and they also usually are roommates. Thankfully, this kind of story eventually lost its popularity and a lot of deconstructions were written.
 * Axis Powers Hetalia fandom is full of works regarding current and past politics and unions. This is (obviously) pretty much only feasible in this continuity, considering that the show is about personified countries.
 * The "Letters" trend: characters answering fanmail being sent to them (via reviews by readers). The strange thing about this is the fact that A) these typically don't require/have an actual plot, and B) interactive fanfic is actually against the rules on FF.net, but they manage to make up a VERY prevalent chunk of the APH category there. Occasionally Did Not Do the Research shows up, since some feature countries/cities/places that the authors do not hail from/have been to.
 * An APH fanfic writer's motto could practically be "If you look hard enough, any pairing can be historical." And it's generally true.
 * The APH fandom is infamous for its Mpreg. Any geographic or administrative region could potentially have its own personification, and for some fanfic writers, there's no better way to Hand Wave in an OC than by having two characters go to town. America tends to get this treatment most often, but search in the right place and you will find Mpreg for any and every Hetalian.
 * AU fanfics with the characters rewritten as ordinary people instead of countries are especially common, since they allow the author to write certain pairings/situations without any of the political/historical stickiness.
 * A good 95 percent of The Cat Returns fanfiction has Haru remaining in/returning to the Cat Kingdom, becoming a cat, and marrying Baron, Completely Missing the Point of the original film. More often than not, these stories will pay little regard to Haru's single mother with no other children who is now alone in the world.
 * In Dragon Ball Z fanfics centered around Gohan like to feature him in high school, where Videl tries to expose him as Saiyaman, and, through a bunch of events that never happen in canon, falls for him.
 * It is common to see Bulma/Vegeta stories that expand upon the events at Capsule Corp during the three year Time Skip before the Android's arrival, in an attempt to pace and/or explain the circumstances of Trunks' eventual conception. Frequent tropes involved within these are the Florence Nightingale Effect, Angel-Devil Shipping, Opposites Attract, and a good bit of Break the Haughty. Most humor is often gathered from the grumpy Proud Warrior Race Guy Vegeta's Fish Out of Water and Alien Among Us experiences.
 * Sailor Moon: Mamoru abuses Usagi or dies. Usagi runs to Demand/Haruka/SEIYA. ChibiUsa is either handwaved into a new child or ignored outright.
 * Alternatively, Mamoru abuses Usagi but she still stays with him for the good of the world and to have ChibiUsa. She then has an affair with Demand/Haruka/Seiya.
 * Usagi and Seiya's bastard child goes to the past/Earth to learn about her history (and accidentally get her parents back together)/purposely get her parents back together/stop her own birth.
 * ChibiUsa comes back from the future as a chesty teen and is much more badass.
 * Usagi is betrayed by Mamoru and/or the Inner senshi. She joins the Outers or Starlights, romances Haruka or Seiya, and is suddenly totally badass/capable/intelligent.
 * One that was popular in the early days of the English fandom: Amara abuses Michelle. Gary Stu arrives to tell Amara off and rescue poor, vulnerable Michelle from the "sin" of homosexuality. (Extremely discredited nowadays. Don't write a fanfic like this unless you want to be nuked from orbit by the rest of the fandom.)
 * Death Note fanfiction not only has its two overwhelmingly popular pairings of L/Light and Matt/Mello, but also predictable storylines of just how they get together. L and Light frequently fall in love during the Yotsuba arc, often with special attention paid to the anime-only rooftop rain scene and averting the canon outcome of the 13-day test.
 * Matt/Mello fanfics often include a teen romance (perhaps unconsummated) in Wammy's House, Matt's heartbreak over Mello leaving to join the Mafia, and then later include angst over . If the fanfic is non-angsty, Matt/Mello often appears as a secondary couple in a Ship Mates fanfic along with L/Light, with all four working as detectives together and getting along surprisingly well, despite Light being a (possibly reformed) serial killer.
 * Light complains about L eating so much sugar and not letting him sleep. L complains about the time Light spends on personal hygiene.
 * Light and L forget that they are working on a high profile murder case and are paranoid neurotics and go to the movies / beach / mall / candy store / fun place for no good reason.
 * Light forgets that he's on a righteous crusade to eliminate evil and because of the power of twu lub gives up the notebook to be with L.
 * Mr. Yagami gets mad at L or Light for sleeping together.
 * Misa is a hateful bitch and tries to kill L and/or Light.
 * For the rare het fic: Misa is a stupid puppet that does whatever Light tells her.
 * Light is an abusive ass, Misa falls in love with L, and Misa or more commonly Rem cuts a deal with L.
 * Mello gets into a fight with Matt about lack of chocolate or ignoring him in favor of his video games.
 * Beyond Birthday arrives to rape/dismember/kill L, Light, Mello, Near or whatever Woobie of choice.
 * Light becomes a Shinigami.
 * Light develops Dissociative Identity Disorder.
 * Rewrite the show so that Light never picked up the notebook.
 * L's Backstory is finally revealed. It's very dark and tragic.
 * Matt saves the day.
 * Mello lied about having no interest in Sayu. Sayu is raped by the mafia guys. Or Mello saves her to rape her himself.
 * A Mary Sue with a tragic past falls into the Death Note world from our world and derails the plot with her charms.
 * A Mary Sue with a tragic past arrives at Wammy's House but eventually gets kicked out for being smarter than everyone else and goes on to pair up with the character of choice.
 * A Mary Sue with a tragic past has a super special Life Note and the Eyes and a Shinigami buddy at her side and goes on to pair up with the character of choice.
 * In Fruits Basket fandom there's the 'wolf of the zodiac' story. A new animal (usually a wolf, cheetah or other 'cool' animal) is added to the Eastern Zodiac. This is almost always a girl.
 * In Yu-Gi-Oh! fandom, a huge amount of Kaiba/Jonouchi fanfiction seems to be about how the mighty Kaiba rescues poor, defenceless Jonouchi from his abusive father, often finding him beaten half to death in a dark alley. He then offers him to live with him "temporarily". You can probably imagine how this one ends. Expect Jonouchi's True Companions to be suspiciously absent.
 * It's rather popular to bring Atem back from the dead (explained or not) for shipping purposes. Generally with Yuugi, but other examples do exist.
 * A common plot in K-On! ero-Doujinshi is one or more band members having sex in the club room, and somebody else spying and/or walking in on them. Western fanfics frequently use the following plots:
 * The school becomes co-ed so that a male Author Avatar can join the cast.
 * Ritsu becoming sexually irresistable when she takes her headband off.
 * One or more characters' parents disapproves of them being lesbians. (Nobody seems to want to write a scene that actually depicts the characters coming out to disapproving parents: it either happens offscreen, in backstory, or the fic dies before getting to that point.)

Comics

 * Spider-Man has One More Day Fix Fic (usually involving either Peter or MJ fighting off Mesphito in an Ultimate Showdown of Ultimate destiny). Fics where MJ gets powers (usually Spider related) are fairly common too.
 * Spider-Man, or really any comic book character, Ultimate Universe-style retellings of the series.

Film

 * Labyrinth fic tends to have a few main flavors: A) Sarah will get wished away by Toby/her parents/her roommate/ect. putting her in Jareth's clutches or running the Labyrinth again. B) Jareth with get all possessive and try to whisk Sarah away as his 'bride'. C) Either Jareth or Sarah is in Big Trouble and the other has to help him/her out. Romance Ensues from all these 99% of the time, & they are handled with varying degrees of subtlety.
 * The Hangover fics have a very high tendency to have a previously unmentioned sister or female cousin of one of the four guys (usually Doug) join up with them and get involved involved with Alan, or more rarely Stu or Phil.
 * In fanfic for Star Trek XI, the idea that Kirk received some of Spock Prime's memories of his friendship (or "friendship") with Kirk Prime during the mindmeld on Delta Vega is particularly common—especially among Kirk/Spock shippers.
 * Fanfiction for The Incredibles is inordinately full of stories where Syndrome returns, kidnaps Violet (her specifically, instead of Jack Jack like he pledged he would) in order to get his revenge, only for the two to fall in love with each other with either Syndrome turning good or Violet turning evil.
 * Tron fanficcers: Admit it, we've all got our own guesses about what happens to the title character after his involuntary dunk in the Sea of Simulation.
 * The Disney's Hercules fanfiction community has stories introducing Persephone, the Goddess of Spring and the traditional Queen of the Underworld, into what is most often a sequel to the movie. She and Hades always get their mythology canon Happily Married status by the end. The Trope Codifier for most of these was probably Hope Springs Eternal.
 * Given that it is already The Theme Park Version of Greek Mythology, certain parts of the story considered “unsavory” to modern palates (such as Persephone being both Hades’ niece, daughter of Zeus and Demeter, and a teenager) are reworked or ignored according to the wishes of the author.
 * And the whole “abduction and marriage” situation is either turned into more of a mutual decision between the two, for Persephone to escape her My Beloved Smother, or kept intact and made to work with the movie’s interpretation of Hades as a suave villain full of schemes.
 * Persephone herself, though stuck in a couple of background scenes for the movie (pink-skinned, blonde curls, huge petal hat), is nearly always given original looks and personality depending on what the author wants to see or feels fits with Hades’ already established character.

Harry Potter
Harry Potter fandom has such an enormous fanfiction community, with so many common plotlines, that it's difficult to keep count:
 * Harry/Draco stories invented the Male!Veela Fic. May be stretched to apply to other pairings.
 * Within the Male!Veela Fic, it's not uncommon for veela!Draco to have a predetermined mate (and it's always called a "mate"). These seem to focus more on Hermione or a new character, either way, she'll put up token resistance before realizing how awesome and sexy Draco is.
 * Harry is sorted into Slytherin, Hufflepuff or Ravenclaw instead of Gryffindor. Slytherin is by far the most common. Expect Draco to be Harry's best friend while most of the Gryffindors, especially Ron, are dumb jocks at best and outright evil at worst.
 * Hermione finds out that she's an adopted pure-blood and, of course, drops her adoptive family like a hot potato in favour of the new, improved version. Her new family will invariably be aristocratic and on the same social plane as the Malfoys, often resulting in her befriending Draco if not romancing him. Her newfound wealth, especially the clothing, will be described in loving detail. She will get a complete personality transplant, sometimes with the added feature of an Unnecessary Makeover, causing her to abandon her old friends and more critical reviewers to wonder why the author didn't just use an Original Character.
 * If she's shipped with Draco, there's a good chance it's the result of a marriage contract.
 * Occasionally she's revealed to be Draco's twin sister, in which case, she's usually paired with Blaise Zabini.
 * The gang, in whole or in part, time-travels to the time of the Marauders.
 * Sometimes, they go back to read the seven Harry Potter books to them (excluding Peter). Basically a MST being performed by the Marauders of the original Potter books as though they were fiction for the Marauders.
 * Oh, and a good number of the Marauder MST fics tend to assume that Marauders are still at Hogwarts and yet somehow find nothing at all odd about more modern things that the books talk about. Not that are many, admittedly...
 * Stories in which Hermione alone is sent back in time and later falling to fall in love with Remus or Sirius or Snape used to be very popular circa 2005 to early 2007, but have since all but vanished. (It's not a bad concept, as long as that's not all that happens. Hell, Voldemort had been working on his power base for almost thirty years by the Marauder Era.)
 * Similarly, a (usually) female character is sent back in time to redeem Tom Riddle with sex. This probably started as a way for Tom/Ginny shippers to get around the whole him-being-future-Voldemort thing, but now it's done almost as often with Hermione. And, of course, it was also done with a certain Mary Sue in My Immortal.
 * A variant was also done in Child of Grace, except that the author skipped the sex and just had the memory Riddle be a nice guy all along, in no way responsible for the evil actions of his present self (ignoring things like by the time he made the journal he had already released the Basilisk).
 * In response to the medical finding that Purebloods have become so inbred that they have reduced fertility rates and/or are likely to give birth to Squibs, the Ministry of Magic establishes a Marriage Law which forces Muggleborns (and sometimes half-bloods) to marry pure-bloods. Often the law is actually a ploy enacted by Voldemort supporters/sympathisers still in power to punish or neutralise the heroes of the second Voldemort uprising. Almost always ends up pairing Hermione with Snape (since the concept originated as a fanfic-writing challenge on a Snape/Hermione mailing list), but sometimes includes other pairings. Since then, Draco has become the most common.
 * Despite Snape beinga half-blood, prior to Half Blood Prince it wouldn't have been entirely unreasonable, given Snape's former Death Eater status, to assume he was a pureblood. The Marriage Law theme originated during that time period and just kept going after being Jossed.
 * If he isn't ignored entirely, addressing how Hermione already marries a pureblood has its own common explanations, either Ron insisting that she pump out endless babies just like his mother, Ron suddenly turning evil, or "Ron marrying Hermione to protect her from Draco's marriage contract would make the Malfoys REALLY MAD! Only Snape is strong enough to protect her!"... which doesn't really make any sense. Harry, being not technically Pureblood, is not an option. Sometimes worse options are brought up as possibilities.
 * Some Marriage Law fics state that partners will be chosen by the government. One fic even included a statute that the marriage must be proven consummated within a certain window of time.
 * This scenario often involves Hermione's extensive use of the Time Turner in book three making her half-a-year or more older, to make her old enough to qualify for being forced into marriage. (Forgetting/Ignoring that this is kind-of cancelled out by the time she spent petrified in Chamber of Secrets, and that she was only allowed to use it to attend classes that clashed with others (Divination and Muggle Studies), which adds up to two weeks at most.)
 * Harry has a twin, and it's he or she who is the real Boy/Girl-Who-Lived.
 * Alternately, the twin is hailed as the X-Who-Lived, while Harry is both the real Boy-Who-Lived and ignored.
 * A For Want of a Nail outcome, where Neville Longbottom is the Boy-Who-Lived, is explicitly mentioned by Dumbledore and Harry at one point hypothesizes what such a world would be like, practically screaming to be used.
 * A distant (in terms of blood or just geography) relative discovers his or her connection to Harry, and rescues/adopts/comes to the aid of Harry. Again, fodder for crossovers.
 * Harry is framed for some horrendous crime and is imprisoned in Azkaban. Eventually he is either cleared or escapes, but not before the experience grants him an immense powerup, which he mostly uses to enact his revenge on those who betrayed or framed him, as well as defeat Voldemort (if the two aren't one and the same). All of his friends will turn on him, including Sirius, and often one of them will kill Hedwig and rip up his photo album, then laugh about it afterwards. (In other words, The Count of Monte Cristo ) They're almost always awful.
 * After Voldemort wins (or worse, after a Pyrrhic Victory over Voldemort that leaves Wizarding England a depopulated wasteland), Harry goes back in time in some way to his school days so that he can use his foreknowledge to craft a better outcome. Occasionally a different character will do so.
 * A Very Potter Sequel has a kind of reversed version of this, with the bad guys trying this to undo the happy ending.
 * The "Dursleys abuse Harry" fanfic. In these fanfics, Harry's Hilariously Abusive Childhood is treated much more seriously. Expect rape to occur. Other common features of these fanfics:
 * This new level of abuse will not be retconned as having been happening all along. Instead, it will start when Harry is a grown teenager with wizard friends and a supposedly murderous godfather. Usually, Harry arrives back at Privet Drive for the summer and, for whatever reason, the Dursleys immediately decide to start beating/raping him. Often the catalyst is Moody's threats at the end of the fifth book, with Vernon developing a "they can't tell me what to do" attitude in response. Expect the story to begin In Medias Res, with a beaten Harry thinking back on how different the Dursleys have been this summer.
 * Vernon is entirely responsible for the abuse. Petunia and Dudley will be mentioned so little you'd think Vernon and Harry were the only people living in the house. If Petunia and Dudley do participate in the abuse, they'll essentially be Vernon's minions. Alternatively, Petunia has a Heel Face Turn.
 * Harry is given an impossible list of chores, which is he beaten/raped for failing to complete.
 * Harry is once again forced to live in the cupboard under the stairs.
 * Vernon brutally kills Hedwig so Harry can't contact the wizarding world for help.
 * Harry is rescued by someone, usually Snape. Thus, the abuse may be setup for a Hurt Comfort Fic. Alternatively, it's setup for an evil!Dumbledore fanfic.
 * Hermione and Draco are Head Boy and Head Girl in their Seventh Year, which means that.
 * The "Head Boy and Girl's private quarters" plot device, where they have to share a suite of rooms, providing lots of forced interaction to fuel sexual tension. Used for Seventh Year Harry/Hermione and Ron/Hermione fics, Hermione/Draco Foe Yay, and even fics with a Mary Sue or Gary Stu paired with Harry, Ron, Hermione or Draco, and originated with the once-popular Percy/Penelope ship.
 * Most oddly, this is so codified that it seems to have been forgotten that the Head Boy and Girl are actually supposed to be top students. Instead, fanfiction makes it look like the selection of Head Boy and Girl is completely random. No one ever even wonders any more "How did Draco Malfoy get to be Head Boy?"
 * This device also turns up a lot in Lily/James fics as well as fics set in the Next Generation (usually with Rose/Scorpius).
 * The Yule Ball is restaged despite there being no Triwizard Tournament, sometimes with a Hand Wave and sometimes without. Hilarity and romantic hijinks ensue. Oh-so common before Order of the Phoenix—even The Draco Trilogy used it at one point. Apparently, it took the release of Phoenix for fanfic writers to finally grasp that the Yule Ball is not something that happens every year. Oddly, Potter Puppet Pals used this years after Phoenix when Snape writes in his diary about being at the Yule Ball with Lily Evans, although he was describing a dream he had had.
 * Harry and Ginny (or Harry and Hermione, or Harry, Hermione and Ginny, or Harry and Luna, or Harry/Anyone, or Harry/Everyone) discover they have a Soul Bond linking their hearts in eternal Twoo Wuv and their magical cores in eternal Badass.
 * There's a school class which pairs the characters to learn how to be grown-ups, normally by making them live together as a married couple in the Room of Requirement, take care of a magically created baby, and (of course) fall in love. Because putting hormonally fuelled teenagers together, and making a child you plan to delete in a couple of months, isn't morally wrong. At all.
 * Hermione, Ginny or a Mary Sue becomes a maid in Malfoy Manor. Where Draco lives. Do you see where this is going?
 * Turns out the Marauders weren't the real pranksters of Hogwarts. Oh no, it was Lily and her band of female friends, who were Just As Good As The Guys If Not Better. Lily joyfully out-pranking the Marauders would seem to contradict the fact that she canonically considered their pranks cruel, but that has not dissuaded anyone.
 * Lily's band of female friends appears a lot in the Marauder-era fics anyway, pranksters or not, at least in the Finnish Harry Potter fandom. Usually, the group includes a beautiful, loud, extremely popular girl and a more soft-spoken, very smart girl, who are paired to Sirius and Remus respectively.
 * Before Order of the Phoenix revealed more about Arabella Figg she was often portrayed as Lily's best friend and Sirius's love interest.
 * Harry's real father is Severus Snape, not James Potter (despite canon repeatedly saying that Harry looks almost exactly like his father did at the same age. Sometimes this is Handwaved, more often it's just ignored.)
 * Funny thing about this one. Like the Marriage Law fic, it was initially popularized by a challenge. These fics are often called Severitus fics, after the Severitus Challenge, which was issued in 2001 by, you guessed it, Severitus. The original constraints of the challenge called for Harry's appearance to gradually change to resemble Snape's over the course of the fic, with the idea being that his original appearance was the result of a potion/glamour/whatever. (They also called for Remus to come back to Hogwarts at some point.) The challenge was extremely popular, and the name stuck even after people started to drop some of the requirements. (Sometimes people call just plain old "Snape is Harry's father" fics "Sevitus" fics.)
 * For some reason, the characters decide to play the inane children's game Truth Or Dare. Or alternatively Strip Poker. The results are pretty much the same either way.
 * One of the male characters is temporarily/permanently turned into a girl. Expect no explanation for why re-applying the same spell wouldn't change him/her back. Often leads to the literary equivalent of a Shopping Montage after which the story turns into a Dead Fic since the writer inevitably didn't have much of an idea beyond "let's make Harry/Ron/Draco/Sirius/the giant squid a girl!" Alternatively this is done to pair him with another male character without it being a Slash Fic.
 * The "Founders Fic" is a whole Harry Potter sub-genre unto itself. Predictably, depending on the author's house preferences, Gryffindor and Slytherin are either Idiot Hero or The Cape (trope) and either Smug Snake or Tall, Dark and Snarky, respectively. Often they're best friends who have a falling-out. Ravenclaw is typically a beautiful Brainy Brunette and sometimes a Rich Bitch. Hufflepuff has Hair of Gold and is a motherly, closer-to-Earth farm-girl type. Several of these things turned out to be canon in one way or another, but they're all older than their respective confirmations in the books.
 * My kingdom for one, just one fic where all four of them are portrayed as scholars who could reasonably found a school.
 * Ron the Death Eater, a situation so common it became the Trope Namer for the entire general phenomenon: Ron is so jealous and resentful of Harry that he spontaneously does a Face Heel Turn. Often a result of Harry/Hermione shippers wanting Ron to Die for Our Ship. Alternately Ginny's been dosing the pair with Love Potion to steal Harry's money and fame. Or Hermione's the one doing it.
 * Most of the Tom/Ginny fics written by shippers who don't mind the extreme age difference between the two or that Ginny is barely 12 can be summed up as "Tom Riddle has sex with Ginny in the Chamber of Secrets before Harry shows up".
 * It's not so much the extreme age difference as the fact that Ginny is barely 12. (And the myriad other ways the 'relationship' would be wrong even if she was older.)
 * Harry and/or Hermione go to Australia to retrieve Hermione's memory-wiped parents and complications arise.
 * No one starts Hogwarts at the age of eleven anymore. Instead, original characters seem to stop by Hogwarts just for their final year so they'll be old enough for teen romances (and, presumably, so they'll be closer in age to the author). Sometimes there is a Hand Wave, often along the lines of she already knows everything she needs to.
 * Usually set post-Order of the Phoenix, Harry stays over at Hermione's house for the summer and notices that she is getting Curves in All the Right Places, and they fall in love (and usually have sex) with each other very quickly. To make it even clearer that the story is a blatant Harry/Hermione One True Pairing, there will either be another prophecy uttered or that was hidden so The Power Of Their Love will defeat Voldemort, or Ron and/or Ginny's characters being changed or turned evil to remove them as Love Interests.
 * The same basic "Summer of Love after Fifth Year" theme is done quite frequently, with almost every thinkable female character from the series: Ginny, Tonks, Susan Bones, ...
 * And in the case of Tonks, she is usually assigned to be a guard near Harry's house (mainly as an excuse by the author to have her there) and quickly grows sympathetic to his guilt and sadness over Sirius's death. Within the two months before going back to begin his sixth year, they'll have completely fallen in love. The fact that she is six or seven years older than him at this point is often (understandably) brought up by everyone, that is if Harry and Tonks aren't seeing each other in secret.
 * Harry actually didn't save Ginny when he destroyed Riddle's diary. She was actually still evil, but didn't let on. This can go two ways. In the unsympathetic route, this becomes Ginny The Death Eater. And then there's the sympathetic route, which amounts to "Ginny's evil, but that's all right because Evil Is Sexy and now she can be Tom's queen." (The latter type nearly always finds a way to revert Voldie back to his Riddle-era good looks.)
 * Harry discovers his parents' will(s) were never executed (usually because of the machinations of a Manipulative!Dumbledore, and often in the course of receiving his inheritance from Sirius post book five). By various means he corrects this, and becomes filthy rich and a Political Power. (Which is weird, because he's already filthy rich, and he doesn't do anything with it.)
 * Sometimes it will be discovered he gained legal adulthood and hence 'full access' to the vaults (despite him appearing to already have this in the books) and Potter and Black seats on the Wizengamot because he's in the Tri-Wizard Tournament, despite the fact that the Tri-Wiz has included plenty of underaged students before. It's just this time the school administrators rigged a external age line to keep them out.
 * Dumbledore's a Manipulative Bastard setting Harry up as a sacrifice in order to defeat Voldemort (in more extreme cases with Dumbledore planning to take all the credit afterward). But Harry has managed to get emancipated and come into his own, with all the money and political power he needs to thwart both Dumbles and Riddle. In well-done instances, Harry must race to learn who to trust and what he needs to know in order to save himself before Dumbledore's or Voldemort's plans come to fruition; in poorly-written implementations, Harry effortlessly defangs and counters all opposition, leaving them blinking in stupefaction in his wake.
 * This is often combined with "Harry finds his parents' real will" and the "Summer of Love" mentioned above. Expect Harry to end up as "Lord Potter", "Lord Black", or "Lord Potter-Black". In most cases the Weasleys will not be trustworthy, or at least Ginny, Ron and Molly won't be. Expect Harry to end up with Hermione, Luna, or some Slytherin girl that's been mentioned three times in five books. Or all of them at once.
 * In addition to these, Harry sometimes gets a 'magical inheritance' that instantly grants him a Superpower Lottery of magical talents and abilities, with no effort involved. Expect him to be a Metamorphmagus like Tonks, an Animagus (almost always a Phoenix), and have several other skills and 'lost' forms of magic that nobody else in the series has, such as a Golden Patronus. In most cases, he has to go to Gringotts to receive it, which crosses over with the 'Harry-Is-Nice-To-Goblins' plot-line. Yes, he is informed of and given his true power and respected by Goblinkind just because he remembered Griphook's name.
 * Also very common in these fics is to have Ron, and often Hermione or Molly (but always Ron) revealed to only have been friends with Harry on Dumbledore's request. The idea of an eleven year old child pulling off this kind of long-term deception is laughable, and if Hermione is included it reaches the far side of the Xanatos Roulette, given how her actual friendship with Harry began. Finally, it's not uncommon for Dumbledore to be paying Ron (and any others involved) with money embezzled from Harry's own Gringott's account, which would only increase the odds of Harry finding out the truth.
 * Someone (usually Snape) is turned back into a baby or a small child. He then must be cared for by the other characters or, in some cases, one character in particular. All in an effort to make Snape cuddly.
 * In the course of the second task of the Triwizard Tournament, Gabrielle Delacour bonds to Harry and becomes for all magical and legal purposes his wife. Fortunately, due to the vagaries of Veela biology she is not actually the eight-year-old she appears to be, and shortly thereafter undergoes a perfectly normal delayed and accelerated puberty that leaves her physically at her real age of 14 or so. Can be found in both Harry/Gabrielle shipping stories and Harry/Harem stories.
 * Harry discovers he is bound by one or more marriage contracts signed before his birth or in his infancy, requiring him to marry a girl (or girls) he barely knows.
 * Harry's simple courtesies to the goblins of Gringott's mark him as uniquely different from the racist bastards that make up the rest of the Wizarding World, and they throw all their military and economic power behind him.
 * Matchmaker!Dumbledore. Wise, old Dumbledore understands how right the author's One True Pairing is and becomes a Shipper on Deck, dropping irrelevant concerns like killing Voldemort. After all, if Dumbledore says Draco and Ginny should be together, then obviously it must be true, right? Naturally, never combined with Manipulative!Dumbledore because manipulation which brings about the author's OTP is obviously good. Often leads to the "Head Boy and Girl's private quarters" plot.
 * In "Sirius lives/is saved" fics, he and Harry will almost certainly team up to become gentlemen thieves who steal from the Death Eaters and purity-obsessed families to better the wizarding world... and go from wealthy to more money than a god. Often combined with the Harem fics.
 * During the Three Year Summer, it was common to see Arabella Figg turn up as the new Defense Against the Dark Arts teacher, typically with a portrayal as the most badass Cool Old Lady ever. After Order of the Phoenix established she was a Muggle Born of Mages, this plot died a quick death.
 * There's a sect of uber-powerful magical people who basically are to wizards what wizards are to Muggles. They're called Magids in The Draco Trilogy, the Strega in Pawn to Queen, and the Druids in The Girl Who Lived, but it's all the same basic idea. The Strega and the Druids are especially similar, sharing Can't Argue with Elves and Author Filibuster tendencies.
 * In a growing number of fics, these uber-wizards are the witches and warlocks of Bewitched.
 * One of the characters (usually Harry or Draco or Hermione) become an animagus or are transfigured into an animal, and hide in plain sight as another character's pet (usually Harry or Draco or Hermione).
 * The "what if Voldemort won?" fic. This leads to a Dark Fic set in the bleak Dystopia he has created, but all too often it's just an excuse to set up a kinky Lemon in which Hermione is forced to be Draco's Sex Slave or somesuch. Post-Deathly Hallows, the non-lemon versions tend to instead take place during that book when Voldemort did win for certain values of the term, but not permanently.
 * Diary fics where the diary writes back, like Tom Riddle's. Sometimes this is for a villain's own nefarious purposes, like it was in the one canon example, but sometimes they rely on the premise that these diaries are as normal in the wizarding world as portraits that talk.
 * Imagine the advertising for that. 'Hi there, parents. I'd like to put my memories in this book, to live under your daughter's pillow and have her tell me all her secrets, and I'd advise her what to do!'
 * A common one is to introduce a Mary Sue with an additional prophecy. This prophecy usually concerns whether Draco sides with Voldemort or Dumbledore, how only she can guide him in this choice, and how Harry's prophecy is entirely dependent on this one. Expect the prophecy to only use vague terms about "light" and "dark" and animal imagery (Draco is usually the "Dragon," while the Mary Sue is normally the "Phoenix"), despite the fact that the original prophecy didn't bother with obscuring imagery.
 * God!Potter is very common. The general outline usually has Harry returning for his next year at Hogwarts after being trained by Elves/Demons/Time Lords and already having powers far more advanced than anyone in the school. Staples include limitless shapeshifting, wandless/wordless magic, "almost Unforgivable" curses, fluency in a secret language and floating runes. They almost always follow the plot of a canon book, but Harry solves each problem with his new powers while hiding his real potential.
 * Salazar Slytherin is Sealed Evil in a Can and the can gets opened. This usually occurs when a fanfic takes place after the defeat of Voldemort and the author needs a new Big Bad. Salazar Slytherin in these fics is often just Voldemort with a different name, right down to recruiting former Death Eaters as his followers. The Draco Trilogy is probably the Trope Codifier or even the Trope Maker for this plot. Hogwarts Exposed used it too.
 * There's quite a few fics where the Hogwarts students take a mandatory trip to the U.S. Sometimes they're visiting a wizarding school in the States, and other times it's just a plain old Muggle school.
 * Everywhere Else Is Full: A common trope in both the original books and fan fiction. Whoever gets top dibs on Hogwarts Express compartments, it's not main characters. Inevitably, Everywhere Else Is Full, so they'll have to share a compartment with Plot Relevant Character. In the original series, this trope is used to introduce Ron in the first book, Lupin in the third book, and Luna in the fifth book. The exact words "everywhere else is full" are actually spoken by Ron in the first book/movie and by Hermione in the third movie (not the book version). In the world of fan fiction, it's pretty much reached the level of Share Phrase.

Other Literature
"Then at the egging of Androg they left Beleg tied to a tree without food or water... but he said no more to them. When two days and nights had passed in this way they had grown angry and fearful, and most were now ready to slay the Elf. As night drew down they were all gathered about him, and Ulrad brought a brand... but at that moment Turin returned... and he saw the haggard face of Beleg in the light of the brand. Then he was stricken as with a shaft, and tears long unshed filled his eyes... "Beleg, Beleg!", he cried... at once he cut the bonds from his friend, and Beleg fell forward into his arms... At first he gave heed only to Beleg, and tended him with what skill he had."
 * The Sherlock Holmes fandom is peculiarly fond of giving the detective hypothermia.
 * The Dresden Files fandom is really into Gender Bender, particularly of Harry, in an attempt to offset (or at least explore) his sexist tendencies.
 * Another massive trend is the Sex Kitten Harry, taking place in some amorphous time after . They, similarly, offset or explore Harry's canon attitudes on sex (I.E., not having sex with a new partner while still trying to save an old one, not having sex with monsters trying to eat or manipulate you, and not having sex with minors), which the fandom often spins as repressed or even misogynistic. Sense a trend here?
 * The Maximum Ride fandom seems to really like High School AU stories. Understandable, considering what they have to go through on a constant basis in canon, not understandable in that the one time they actually DID go to school, it didn't end well for them.
 * Percy Jackson and The Olympians: Half-blood goes to camp. Half-blood gets amazing powers. Half-blood saves world. Simmer for five minutes. Serves thousands.
 * A Series of Unfortunate Events: the Baudelaires are sent to live with a new guardian, usually an Original Character, although crossovers exist.
 * Writers for The Silmarillion, specifically Maedhros/Fingon shippers, are practically obligated to write hurt/comfort fic based on Fingon's rescue of Maedhros from Thangorodrim. In all fairness, it's pretty much the last moment in the book for them which isn't utterly tragic.
 * If you happen to be a fanfic writer for Children of Hurin, it's almost obligatory to compose a Beleg/Turin hurt/comfort fic at some point in your career. Somewhat Justified, though, with canon lines like this one:


 * The Lord of the Rings, because it's more accessible than the above, has far too many Tenth Walker fics, to the point that they were already being parodied almost a decade ago.
 * Also, fics featuring Faramir or Legolas being abused by their respective fathers are ridiculously common.
 * The Bartimaeus Trilogy: Nathaniel comes back to life and/or is in love with Bartimaeus a lot.
 * Good Omens: Poor Crowley gets mistaken for an incubus quite often in fic.
 * Star Wars Expanded Universe fics where Grand Admiral Thrawn manages to survive his Bodyguard Betrayal are very common.
 * Fics with characters from another fandom put in Lyra's world of the His Dark Materials trilogy, not necessarily involving any characters from the trilogy, so that the author can demonstrate what shapes they think the characters' daemons would be, overlooking the fact that traveling to that dimension will not necessarily cause your daemon to manifest, but being born there will, so it only works as a whole-cloth Alternate Universe. Not the same as Common Crossover, because any fandom can be plugged into this scenario.
 * Roughly 50% of Narnia fanfiction that doesn't feature a Mary Sue will tackle the so-called "Problem of Susan," either making her out to be The Woobie that got screwed over by Aslan and everyone else, or having her  causes her to realize the Error of Her Ways.
 * Tamora Pierce fandom has produced a truly astonishing number of Alanna-goes-to-the-convent fics (in canon, Alanna hated the idea of going to the convent so much that she disguised herself as a boy and learnt how to be a knight instead). Their main purpose seems to be to get her together with Prince Jon, who she dumped in canon.
 * The Hunger Games has an awful lot of 'Random OC who may or may not be a Mary Sue ends up getting reaped'. Some better writers will play with this by not having the character actually win, but as there are only two possible plot permutations the entire thing ends up horrifically overused.
 * And of course there's plenty of Alternate Universe Fics that ask "What if Rue/Thresh/Cato/Clove/Foxface/Marvel/Glimmer/Boy From District 7/etc. had won?" and explore the rest of the trilogy from that character's point of view (or take the events post 74th Hunger Games in a completely different direction).
 * A lot of Darkest Powers fanfiction features werewolf Derek and necromancer Chloe realizing that they are mates. In canon, the only mention of them being mates was made by Liam, who was taunting them. Also, in the main series, the werewolves do have mates... but it's nothing as huge, compelling, or life-changing as it's often made out to be in the DP fanfics. Rather, the only time it's treated as a somewhat big thing is in Personal Demon, when Karl attempts to explain to Hope that the reason he left her is because he was terrified by how completely attracted to her he was (and still is).
 * Warrior Cats: A Clan kit has a prophecy about them. They get apprenticed. They end up fulfilling the prophecy and often become Clan leader at some point.

Live Action TV
"Mary Sue is the youngest officer ever to serve on the starship Enterprise. She is a teenager, tall and slim, with clear skin and straight teeth. If she is not blond, Mary Sue is half Vulcan, her ears delicately pointed. But Mary Sue is not just another pretty face. She is usually highly educated, with degrees from universities throughout the known universe in all fields of technical and cultural studies (or an equivalent head of her class in Starfleet Academy). She can mend the Enterprise with a hairpin, save the lives of the crew through wit, courage, and, occasionally, the sacrifice of her virtue. If the formula is strictly followed. Lieutenant Mary Sue dies in the last paragraph of the story, leaving behind a grieving but safe crew and ship."
 * Fic dealing with Don't Ask, Don't Tell is common in Stargate Verse slash, though there are a few other fandoms where it's possible.
 * And fics dealing with the military's policy against fraternization are also common on the straight side of things, such as Jack/Carter fics.
 * For the Glee fandom, Blaine-centric stories that transplant the characters to a Film Noir setting are common. Blaine is overwhelmingly the sharp-dressed, jaded Private Detective, the New Directions and the Cheerios are rival nightclubs, and Kurt will either be the person seeking help or connected to them in some way. The Kurt/Blaine fics often end very badly. It's hard to tell how much of it is just faithfulness to the film-noir style, and how much is a reflection of real-life Values Dissonance.
 * The badboy!Klaine trend. Blaine or Kurt is Troubled but Cute, and the other is usually very close to their canon persona. Sometimes, especially when Blaine is the bad boy, Dalton is some sort of reform school.
 * A good number of Kurt/Blaine fic reference or incorporate "Baby It's Cold Outside", even before the actual duet was released.
 * An interesting trend is several stories where Rory and Sugar sleep together, and she becomes pregnant shortly before he returns to Ireland.
 * Many future fics involve characters performing together on Broadway. This is particularly common with Rachel/Jesse fics.
 * Sugar, Rory, and Harmony being the children of Brittana, Klaine, and Finchel or Faberry (respectively) travelling back in time to visit their parents. Occasionally they also include Sebastian as the son of Kurtofsky.
 * Many Sam/Rory fics take place either during Christmas (when the ship was first introduced) or Valentine's day (in the Christmas episode Sam promised to be Rory's sponsor and help him get a girlfriend for valentine's day).
 * iCarly: Mostly based around shipping, each ship has a couple specific plots that come up time and again:
 * Sam/Freddie: Having a "Sam gets pregnant" fic is pretty much a rite of passage for any writer. A writing challenge which constantly flooded the site until the end of 2010 was the pair ending up as the lead in a romantic play, usually Romeo and Juliet. Fix Fic reworkings of the episode iSpeed Date.
 * Carly/Freddie: The "Root and Berry Retreat" fic for Creddie (Carly/Freddie) writers in the back half of 2009. Fix Fic reworkings of the episode iKiss.
 * Sam/Carly: Sam is a lesbian, Carly isn't; Hilarity Ensues, as does If It's You It's Okay. A smaller but significant variation involves Carly as a lesbian while Sam isn't.
 * Odds are, any White Collar fic will either have some sort of Ho Yay between Peter and Neal or at least some Neal whumpage. Based on these, it's hard to believe Neal can cross the street without a) breaking something b) getting kidnapped or c) getting some sort of disease of illness that requires Peter and Elizabeth take care of him.
 * Back in 2005/2006, probably a good fifth of all Criminal Minds fic involved Reid being kidnapped and tortured. It was so common that people wrote parodies of it. Then the show itself used that plot, and it became less popular in fanfiction.
 * Within Torchwood fandom, a truly mind-boggling number of Jack/Ianto Hurt Comfort Fics involve the characters showering together—often not even romantically, but simply because one or the other is hurt and needs help, or is untrustworthy and has to be watched.
 * It seems as if there is no one who hasn't written the "Countrycide" follow up fic.
 * Lots of Fix Fics were written after Children of Earth, either changing the end so Ianto (and occasionally Steven) doesn't die, or bringing him/them back to life somehow. Time Travel is sometimes involved.
 * Heroes Mohinder/Sylar fans have The Road Trip. It's amazing how much fic there is set in those, what? Three days? Of course, give the nature of their relationship, if they ever secretly had sex, that's when they did it.
 * Buffy the Vampire Slayer:
 * The (in)famous Yet Another Halloween Fic sub-genre of fanfiction, in which Xander (and possibly other characters) choose a different outfit for the fateful Halloween when Ethan Rayne turned everyone into their costumes. Invariably, these will be the costumes of recognizable characters, particularly from anime.
 * What might be termed the "Slayer Speculation Fic", in which the famous, strong female character of the author's choice from another fandom is called as a Slayer by Willow's spell in the series finale.
 * A number of stories portray Xander as still having the essence of the hyena spirit inside of him. It seems to often draw him to Oz or Spike, one being a werewolf, the other being a dominant predator.
 * There are three standard Willow/Tara plots:
 * 1) Rewrite season four to show all the details of how Willow and Tara fell in love. (The TV show didn't show this.)
 * 2) Rewrite season six so that Tara doesn't die.
 * 3) A post-season six story in which Tara comes back from the dead.
 * Buffy and Firefly is such a Common Crossover that such stories have their own tropes. For example:
 * Book is (or was) a Watcher.
 * River is a Slayer, and the Academy was a corrupt version of the Watcher's Council. (Well, more corrupt than usual.)
 * Rarely will more than one or two of the Scooby Gang feature, and it's usually Xander or Willow transported to the future/an alternate dimension via magical portal or suspended animation.
 * Xander is an enormous Badass, since he only has normal humans to fight, and has spent his life surviving against creatures at least twice as fast and strong as he is.
 * Mal will be mistaken for Caleb. Zoe and Jayne's resemblance to Jasmine and Hamilton may also be brought up, but this occurs less frequently.
 * Rewrites of season 1-4 episodes to include Dawn, or specifically the altered memories of the cast that include Dawn.
 * The "Skinner finds out about Mulder's and Scully's relationship" stories in The X-Files fandom. (Which is kind of odd, considering he dropped hints several times in the last two seasons that he already knew about their relationship. Then again, so did everyone else...)
 * If you write for How I Met Your Mother and you like Barney/Robin, you have written an episode tag to "Benefits" and/or "Sandcastles in the Sand".
 * Power Rangers stories that feature Tommy post-Zeo have two options: tackle the reason for the infamous Dear John letter that caused Tommy and Kimberly to break up, or completely ignore it. Fans have since gotten very tired of new stories that choose to tackle it, to the extent that even season 12, Dino Thunder, which brought Tommy back as an active Ranger, completely ignored his romantic past. Stories that feature Kimberly have no choice but to tackle it, unfortunately.
 * An equally captivating problem for the fans is that of Tommy and Kat, as a Flash Forward episode outright shows them as eventually marrying, which makes the lack of any mention of her and of any implication of Tommy's romantic life from Dino Thunder a complicated issue for 'ficcers to address, as most take the earlier episode as gospel truth.
 * A subset of Charmed fanfics are known as "Chris revelation fics", which alter how his true identity is revealed, invariably in ways which increase the drama and/or angst level compared to canon. "Almost obligatory" for a writer in the fandom to have written such a story.
 * There's a related subset, often the same fic or a sequel to one of the above, which allows Chris to in some way
 * If you're a House fan who likes House/Wilson and Dark!Wilson, it's almost obligatory for you to write a post-Wilson's Heart fic where Wilson loses it after Amber's death and takes it out on House, who is either so brain-damaged or so guilty that he doesn't fight back.
 * The Doctor Who episode "Doomsday" spawned hundreds, if not thousands, of 10/Rose Reunion fics, an event which became canon with "Journey's End". After that, everyone is writing the 10.5-and-Rose-in-the-alternate-universe fic.
 * It seems you don't actually get your Doctor Who fanfic writer's union card until you've written an "Eighth Doctor fights in the Time War and/or Ninth Doctor regenerates in the Time War and/or both angst about the Time War" fic.
 * More like Fandom Specific Title, but the Literary Allusion Title "World enough, and time" is practically irresistible to Whofic writers.
 * So you have a story. In it, the Doctor lands the TARDIS on Earth near where you live and meets a human with an inexplicable resemblance to you. He decides this human will be his new companion and the two of them go off to have wacky adventures together. Congratulations, we'll add it to the pile.
 * Stories in which Donna recovers her memories are quite common, usually taking place either at the end of her life (usually elderly) with the Doctor visiting her one last time, or by miraculously being able to remember everything without her mind burning itself up in the process. The latter is accomplished by the Doctor figuring out some clever way to save her that he didn't before, or by regeneration.
 * Fics where the Doctor regenerates into an eight year old/an animal/a girl/pretty much anything else.
 * River Song's true identity used to be a mystery and many different scenarios and theories were written about it, usually by somehow making her be a future version of a companion, namely Rose Tyler, Donna Temple-Noble or Amy Pond. While they significantly died down since the events of "A Good Man Goes To War" and "Let's Kill Hitler", Alternate Universe Fics are still being written that ignore some or all the events of those episodes.
 * Also relating to River, "Forest Of The Dead" Fix Fics are common, as well as fanfics involving her and the Doctor going to the Singing Towers.
 * Fans of The Sarah Jane Adventures like to have an earlier incarnation of the Doctor, usually the third or fourth, although any will do, show up at Sarah Jane's house.
 * With Jeeves and Wooster being such an innocent series, there's a good handful of fics involving Bertie discovering the concept of sexuality.
 * Supernatural: Dean and/or Sam is turned into some kind of monster; one of them isn't a Winchester, so they can be paired safely; a character from another fandom turns out to be their sibling; female equivalents to both brothers are introduced; Dean is also one of the special children.
 * A demon summoning calls forth a character from another fandom who does not behave the way demons in Supernatural usually do. Ex: An attempt to summon "the Morning Star" results in Dawn appearing, dressed up like The Devil for a Halloween party. Or cultists call upon "the Yellow-Eyed Demon" and get Crowley.
 * One of the Winchester brothers gets turned into a dog, usually Sam.
 * If you ship Dean/Castiel and are willing to write a sex scene, you've written a fic set after 'Free to be You and Me'.
 * Top Gear crack fanon considers the Stig an alien with Reality Warper powers. This means that "The Stig did it" is an incredibly common explanation for wackiness in crackfic. Sometimes Top Gear Dog or May's cat gets the blame.
 * For some reason, any Star Trek the Original Series Kirk/Spock author worth their salt has written a, if not several, fic(s) featuring the duo in a cave. The "Kirk and Spock are in a shuttlecraft together, it crashes on a godforsaken planet, they hide in a cave, and Spock goes into Pon Farr" plot has even become a Dead Horse Trope in the fandom, parodied by Genre Savvy fans with the "rude person" meme.
 * Kirk/Spock fics set immediately after "Amok Time" are extremely common, using the idea that the shock of "killing" Kirk didn't stop Spock's pon farr so much as postpone it. And now that he doesn't have a wife to mate with...
 * The Mary Sue plot. At one time, the term "Mary Sue story" referred to the specific plot parodied by A Trekkies Tale. This plot was once very common, but is now largely forgotten. The character in the story would be recognized as a Mary Sue by modern standards, but it's much more formulaic and Trek-centric. The 1992 book Enterprising Women: Television Fandom and the Creation of Popular Myth defines it as follows:


 * Law and Order Special Victims Unit: It's not entirely surprising that many, many Alex/Olivia fics write the missing scene from "Ghost", because the preceding scene deliberately written like that to cheer the shippers up, and then left it nice and ambiguous what it was that they were doing, all by themselves in a hotel room after a meaningful conversation about being someone you're not. Hoo, boy...
 * Merlin fandom is very fond of stories that have the title character reveal his magic to Arthur and/or the rest of Camelot, intentionally or otherwise. These are mostly written since the series has Status Quo Is God in full effect in regard to this, until most likely the eventual Grand Finale (nearly everyone who finds out about his magic tend to end up soon Put on a Bus or dead).

Video Games

 * Gears of War fandom has a few very predictable plots that closely resemble the following: Girl (almost always a Mary Sue or a Jerk Sue, but always a Tsundere) joins Delta Squad. It turns out she's usually like either an awesome stranded badass or the greatest sniper ever in 70% in cases (the other 30%, she's just a random woman who turns badass the moment she starts tagging along with Baird). Then, she falls in love with Baird, have a brief Slap Slap Kiss relationship buildup (sometimes literally), and then ultimately Baird falls in love with her and they have sex.
 * Fire Emblem the Sacred Stones fandom is in love with the "Seth and Eirika angst over their social positions and how it affects their love for each other, but end up together anyway because they're soul mates" plot.
 * From the seventh game, we have lots of people writing novelizations that include the tactician, and fans of the Tellius games have written lots of "What if Soren was raised by his parents?" fics.
 * It's a running joke in Metal Gear fandom that everyone has to write at least one "Tankerfic"—a fic about the alluded-to-but-never-elaborated-upon scene in Metal Gear Solid 2 where Otacon pulls Snake out of a shipwreck in the middle of a raging storm.
 * ARF (Aeris/Aerith Resurrection Fic) for Final Fantasy VII.
 * The Mega Man X fandom contains a ton of stories about Dr. Cain completing one final case before either retiring or dying.
 * Mass Effect fandom has quite a few variations of Samara's loyalty mission since the second game came out, but the chief plot of such stories is either 'the love interest voices disapproval with Shepard being the bait' or another character entirely -usually one of the other squaddies- takes Shepard's place instead. Both styles of this plot are commonly seen with the Female Shepard/Male Love Interest combo.
 * A fairly common plot is Shepard having a brother or sister that either joins the group or takes over when the in-game Shepard dies in a battle somehow, despite one background explicitly saying Shepard is an only child and the other two saying that Shepard's entire immediate family is dead.
 * One type of story that has gained some traction in Dragon Age fandom is having one or more of the other origins meet up with the Warden character and in some instances, have them join the group. (example: a Dwarven Commoner meets a Human Noble and the dwarf joins The Warden, Alistair, Morrigan and the gang) They may or may not be Grey Wardens.
 * For most of the Origins, there is the annoying issue that Duncan saved the potential Grey Warden from certain or nearly certain death, rendering their mutual presence problematic from a canon point of view.
 * Unsurprisingly, Dragon Age also has lots of Dark Ritual fics and fanart, usually with  as the, uh, second participant and   and/or him agonizing over the decision. These range from pure angst to smutty hatesex to conflicted tender lovin' to humiliating performance problems to big happy threesomes. One Big Name Fan fancomic artist, Aimo, even collaborated with the game's head writer on a comic based on a deleted scene where   agonizes about it beforehand.
 * Tales of Symphonia has quite a few fanfics in which Lloyd has a twin sibling—usually a female who, at least initially, serves Cruxis. Cruxis!Lloyd fics are also popular, most starting with
 * A common theme for Dimentio/Mimi from Super Paper Mario is him stealing her diary and using the contents to tease her. However, it should be noted that this does stem from a canon incident.
 * Similarly, a fairly large amount of Bowser/Peach fanworks center around the popular question of just what the heck do they get up to while Mario's busy adventuring to rescue her from Bowser's clutches. Or, many also portray Peach as taking a motherly role towards Bowser's eight unruly children. However, this once again is based off of a canon incident (that of Bowser Junior being convinced that she's his mom and even calling her "Mama Peach"). It's actually unknown just how the seven older Koopalings feel about Peach, but the image of them looking up to her as their mom is cute nonetheless.
 * Touhou has innumerable doujins/fanfics detailing the Backstory of the characters, since not many characters have one to begin with, and even if they do it's still pretty vague. By far the two most common recipients are Rumia (so popular that any fan refering to "EX-Rumia" is immediately understood) and Sakuya (serial killer, former monster hunter, or Lunarian being the three main theories).
 * Explaining what happened to the PC-98 characters, especially Mima, is similarly widespread.
 * Detailing the future of characters is also common, as amongst the incredibly long-lived youkai there are a few humans that will die relatively soon. Reimu, Marisa and especially Sakuya (again) are the targets, though Sanae became increasingly popular after her arrival.
 * There is a sub-genre in Touhou fandom that can be called "Outsider fic", with someone (either a character from another fandom, an original character or a self-insert) falling into Gensoukyou and meeting various characters, either amicably or otherwise. Notably, this is entirely plausible, as the barrier that seals Gensoukyou in its own reality is nowhere near as impermeable as it should be (and some of the "accidents" might actually be deliberate abductions).
 * The (mis)adventures of Team 9, an entirely fan-made Cast Herd consisting of child-like "low level" youkai, seems to be required for every significant story, even if only as a background detail. Indeed, the Non Indicative First Chapter of Imperfect Metamorphosis, and ultimately the entire story, is based around them.
 * A large amount of non-shipping Pokémon fics follow this basic formula: Original Character gets a starter Pokémon from the regional professor, which is usually not one of the normal starters since they've all been taken. Original character encounters whatever villain team appears in the region, or either Team Rocket or Cipher if it's a non-game region. Original character defeats 8 gyms. Original character participates in the Pokémon League, usually winning.
 * As a subtrope of both this and After Action Report, the Nuzlocke Comics based stories are a genre unto themselves. It is basically the same as the situation outlined above, except you are actually recording your playthrough of the game, you are restricted in the pokemon you can catch, and Anyone Can Die is in full effect.
 * In The Sims fandom, it's incredibly common for a "Backstory" type fic to be about Pleasantview and how Bella Goth disappeared. It will involve aliens, because the memory that Bella's husband Mortimer and daughter Cassandra have is that she was abducted by aliens. It also is common for it to involve Dina and Nina Caliente, because they arrived the day before Bella disappeared, and because Dina's late husband is Bella's brother. Another common plotline will be to tie Strangetown in somehow, because of the townie in Strangetown that is named Bella Goth. The one neighborhood that consistently is ignored is Veronaville.
 * A lot of Portal fanfic written after Portal 2 involved Wheatley or Chell, even though both are a no-go in the canon.
 * GLaDOS or Wheatley being transferred to android or human bodies for whatever reason—or just making them human and not even bothering with the transfer. This in turn created its own sub-set, with one or both of them being originally human to better facilitate the transfer (note that ).
 * If one is to write a Super Robot Wars Fanfic, the usual standard story will do the following: Write a prologue in the style used by the games (with a list of "Series Represented" almost always included), then the plot will basically proceed with the novelized version of the same type of mecha anime crossover story writing style endemic to the games.

Webcomics

 * Homestuck fandom has the popular "bloodswap", an Alternate Universe What If fic where the alien trolls have different blood colors than they do in canon - blood color being used to determine their place in the Fantastic Caste System and what Psychic Powers they get (if any). The most well-known bloodswap fic is Red Dead Virgo. A few other fanfics (including RDV) do something similar with the human characters where they are raised by different people than they were in canon.
 * Perhaps the most common form of fanfic for Homestuck (or at least the most common fan-adventure), are the ones in which a completely new group of players (human or troll) plays Sburb. A Sburb session is a ready-made framework for a story and canon that the main characters weren't the only humans to start a session (though it's strongly implied that all other human sessions should be doomed to failure and Word of God has declared that the trolls were the only session for their species). Only very rarely does someone actually bother to invent their own race of aliens, despite that being far more likely canonically, and not everyone succeeds in putting a big enough spin on the premise to make it worthwhile.
 * Life after The Scratch is another big one. These generally revolve around the characters remembering or trying to remember their past or alternate lives. In many stoires the trolls are turned human somehow.
 * Fake FAQs for Sburb, based off Rose's FAQ in canon. Originally, many of these fics treated Sburb and the events of Homestuck as a fictional video game that people were writing strategy guides for. Fake FAQ fics then went dormant until they were revived by the story Sburb Glitch FAQ, which eventually started a Fan Verse.

Western Animation

 * An awful lot of Total Drama Island fics crop up that depict a second season at Camp Wawanakwa using Original Characters for the new cast of campers. Sometimes some mixture of OCs and originals are used.
 * Crossovers are fairly common, pulling in characters from other works as contestants.
 * A common theme of Whole Plot References developed, the majority of which involve Twilight (usually using Gwen and Trent or Courtney and Duncan as Bella and Edward, respectively, then later with Gwen and Duncan filling the roll).
 * A lot of fanfics are about a season where reviewers can apply for a spot on the show.
 * Invader Zim has a ton of these:
 * The Tallest tell Zim his mission was a fake (and he believes them for some reason). Zim will usually get angsty, and either a.) kill himself or b.) be comforted by Dib (resulting in either friendship or sex).
 * Dib realizes humanity stinks and decides to help Zim conquer/destroy the planet. Usually results in sex.
 * Tak returns to Earth and she and Dib get together, or else crashes back to Earth and decides to team up with Zim.
 * A new girl winds up in Ms. Bitters' class. She will either a.) turn out to be an Irken and fall for Zim or Dib (despite the fact there's already an episode where that happens!), or b.) be human, believe Dib about Zim and then fall in love with him.
 * Dib kills Zim, or Zim destroys the world, and then angsts about it.
 * Fics based on the unfinished episodes, particularly "Invader Dib" in an attempt to "finish" the series, are common. That the creators were fairly open about what they had planned for future episodes means quite a bit of available material for these.
 * Many stories have an explanation for why Irken babies are created in test tubes: the Tallest don't let Irkens have kids, the Tallest only let the strongest Irkens have kids, the Irkens have evolved all wrong and now they're no longer able to reproduce, etc. Notably this, and the problems it creates, is the basis for In Short Supply.
 * Phineas and Ferb has a lot of stories where Perry somehow becomes a human, and oh, it also turns out he and Dr. Doofenshmirtz are both gay. Often Dr. D is the one who transforms him in the first place, though usually for ostensibly different reasons.
 * It's common to speculate about the boys' respective missing biological parents. This contains a whole subgenre where turns out to be, with various back stories trying to fit this into canon.
 * A lot of fanfics put the kids in school. Since the creators have stated that the series will only cover time off from school, there seems to be a general fandom curiosity as to what school is like for the characters.
 * At the end of Phineas and Ferb The Movie: Across the 2nd Dimension . This has become a convenient plot device for a lot of ship fic writers. The most common variation is that Phineas or/and Isabella remembers somehow (very often, the memory returns to them in a dream), and decides to act on it. Another variation is that Phineas gets Carl to stop long enough for him or Isabella to write down a message to themselves.
 * In the Teen Titans fandom, it's extremely common to see a fic where:
 * Batman or Batgirl comes from Gotham to entrust or request something from Robin
 * Beast Boy turns back into his form from "The Beast Within"
 * Raven's long-lost demonic sibling appears
 * Any and all variations of the High School AU (at least their ages don't need to be changed)
 * Hey Arnold! fic-writers tend to be fond of the "character leaves town for years, only to return much later to the neighborhood and reintroduce their newly mature selves to their old friends". Despite Arnold actually having a ground semi-speculatory semi-canon reason for doing this, this kind of thing usually stars Helga, who always comes back more attractive and more mature, so as to sweep Arnold off his feet.
 * The Jungle Movie, an abandoned Big Damn Movie project where Arnold sets out to find his lost parents in Central America. Not only would this movie result in him finding his parents, but he was also supposed to get a Relationship Upgrade with Helga. Naturally, a lot of fans were anxious to see this project come into realisation, and have made their own versions.
 * Treasure Planet fanfics seem inordinately fond of direct retellings of the movie, except this time there's a plucky female recruit/stowaway/cabin girl who's a Kindred Spirit to Jim and thus can fall in love with him over the course of the story, if she isn't his sister instead. If not a direct retelling, there are also fics where Jim goes on a voyage that is essentially the same as the voyage to treasure planet, accompanied by a female stowaway who is either essentially Jim's personality from the movie (while Jim can play Older and Wiser) or your average Tsundere so she and Jim can have a Slap Slap Kiss romance.
 * The Land Before Time fandom seems to love the plot of dragging a kid from the present and befriending Littlefoot and the gang. In fact, any plot that falls anywhere on the Speculative Fiction spectrum, with the fate of the world in Littlefoot and the gang's hands, is common.
 * Kick Buttowski shipping fics tend to start with Kick and Kendall agreeing to spend a whole day (or even a whole week) together because of a bet or a dare. Naturally, after some initial bickering, they realize they've fallen in love with each other.
 * Young Justice fics enjoy getting a lot of drama over Robin taking his sunglasses/mask off to whoever he's being shipped with.
 * Hurt Comfort Fics involving Wally and his abusive parents, despite Word of God saying they're Good Parents in this continuity.
 * Avatar: The Last Airbender has many common fic plots:
 * Among the regular flavors of Zutara: Katara being kidnapped by Zuko, Katara's season three hatred for Zuko revealing itself to be sexual attraction, Zuko siding with Team Avatar in the Crystal Catacombs, Mai dying in childbirth and Katara comforting Zuko, and Mai and/or Aang turning evil. Katara usually ends up as Zuko's queen in these stories (the flipside of this, Zuko renouncing his title and living at the South Pole with Katara, is rare).
 * Azula escaping from her mental institution to cause trouble. Alternatively, Azula recovering, and either relapsing or slowly becoming part of the Gaang.
 * The Dangerous Ladies, or just Azula herself, kidnapping or capturing Sokka, or they're stranded alone together in the wilderness, and they come to bond romantically.
 * If a fic set after the war isn't based around the gargantuan amount of reconstruction and peacekeeping required throughout the world, then it will casually mention it as if the reader should already know. Indeed, despite the series as a whole ultimately falling on the idealistic side of the sliding scale nearly every fan reaches the conclusion that no, it isn't going to be that easy.
 * The Fairly Odd Parents has a few fanfics about Norm the Genie falling in love with a female genie master Original Character who treats him right. Each of these have their own unique, slightly weird twist. One of them is a Deconstruction of Genie in a Bottle and perhaps several other tropes. Another has an OC that might be an Expy of Megara. Yet another is a Chobits Fusion Fic (with Product Placement). One is a limerick written by Norm the Genie about a Mary Sue named Rebekah Masters, who is Aladdin's sister, owns a keyblade, has many boyfriends (whatever fictional guys the author finds hot) and lives in the Kingdom Hearts world.
 * A lot of stories reflect on Cosmo and Wanda's failing relationship, as well as how they met and how their Anti-Fairy counterparts met. There are many fanfics about Anti-Poof's birth.
 * Kim Possible: Pretty much every Drakken/Shego writer has done a piece dealing with the fallout from "Emotion Sickness" (in which emotion-setting "Moodulators" become attached to Kim and Shego, and for most of the episode they're crazy with love for Ron and Drakken, respectively). So have a lot of Kim/Ron fans, of course, but to a lesser extent because they have considerably more canon to work with.
 * Two common plotlines in Adventures of the Galaxy Rangers fandom are "Eliza's rescue" (at least 4 versions are floating around), and ones where the other three find out about the full extent of the dirty politics and hellish conditions at Wolf Den—usually in the form of some threat to Shane. Queue the Series 5 team making the guilty parties wish they were dealing with Supertroopers.
 * Jem fanfic will create Mockumentaries based on VH-1's Behind The Music, recapping the team's adventures. These range from playing it mostly straight to Deconstructive Parody.
 * Fans of the Mega Man cartoon show often have Protoman leave Wily, usually by him creating Bass as a replacement. And then Bass isn't seen from again.
 * Fanfiction for The Penguins of Madagascar often includes some method of 'fixing' Marlene's lapsing into a feral state whenever she leaves the zoo. This tends to go hand-in-hand with her finally learning that the penguins' adventures are real and joining the team, since her ability to participate in adventures would be severely limited otherwise.
 * My Life as a Teenage Robot has a whole genre of stories about Jenny becoming human somehow, usually to facilitate a relationship with Brad. (Fans never seem to do this if they pair her with Sheldon, for some reason.)
 * Before season 2 of My Little Pony Friendship Is Magic, stories about the mane six having to face the "Elements of Discord", Evil Counterparts to their Elements of Harmony, were quite common.
 * After the second season and the reveal of Discord, personification of chaos and disharmony, stories abounded with Discord escaping from his can again, either to continue to wreak havoc or... somehow falling into Defeat Means Friendship, despite him being the only purely evil character in the entire series. Alternatively, an even worse evil shows up for the mane six to thwart.
 * Crossover fics dealing with other characters getting transported to Equestria, almost always getting inexplicably "ponified" in the process. Doctor Who is the most common victim of this, thanks to a background character who looks like a pony version of the Tenth Doctor.
 * And of course, humans in Equestria stories.
 * The standard plot for getting the ponies themselves into another universe is famously "Twilight Sparkle tests out a new teleport spell, and it goes wrong". It's gotten to where Equestria Daily explicitly points it out when a fic doesn't do this.
 * It's not just "teleport turns into dimensional travel"; when Twilight tries out any new spell in fanfic, things will go south. One fanfic involving Twilight visiting a darker parallel universe had Equestria Daily note that the universe's existence isn't her fault: "Is that even allowed?"
 * It's popular to pit the gang from Friendship is Magic against updated versions of G1 villains, such as Tirac from "Rescue at Midnight Castle".
 * Princess Celestia turning out to be a horrible tyrant, or Equestria being a Crap Saccharine World. Often this will involve the characters being unaware of this, and scolded by some OC for how naive they were.
 * Rainbow Dash having an accident and, irreparably or not, injuring her wings, requring another charcter to care for her (may or may not involve shipping). At one point these were so ubiquitous that Equestria Daily outright banned them. Then there was the actual episode where Rainbow broke her wings and was confined to a hospital...
 * Fluttershy nursing a hurt character back to health (which has some basis, given that she's the Element of Kindness), often overlapping with the above. Even Trixie is in one of these.
 * A popular theme has Twilight Sparkle (and possibly the other members of the mane six as well) turning into alicorns and taking over the rule of Equestria from Celestia and Luna, who have grown tired of immortality.
 * In Derpy fics where she's the mother of Dinky, it'll often center around the hardships of being a single mother and/or Derpy's ditziness.
 * Many a Bonbon and Lyra fics are about Lyra being unable to get a job, as she's a musician in Fanon.
 * "Luna reintegrates into Equestrian society" stories became (and remain) incredibly popular almost since day one, with Progress only being the most well known. Almost all contain some form of The Atoner mixed with Adorkable, No Social Skills and Fish Out of Temporal Water, and most draw some sort of parallel to Twilight's situation, if not outright having Twilight help her adjust. "Luna Eclipsed" confirmed all of these and further strengthened their prevalence, although later ones drop the fan-made meek, submissive portrayal and adopt the official Large Ham portrayal.
 * Any fanfic that is centered on Scootaloo is usually going to make her an object of pity, either it will be about her inability to fly or her lack of any known family. She often ends up being comforted or adopted by Rainbow Dash as a result.
 * Gargoyles fandom: What if Elisa Maza (or any other character) was definitely turned into a Gargoyle?
 * A great many Danny Phantom fics involve the return of Dark Danny. This is largely due to his immense popularity, the fact that he only appeared in the series once, and that supposedly he was going to return if the series wasn't Screwed by the Network. What he does when he returns varies from story to story: sometimes he gets shipped, other times he gets "redeemed," but he usually goes on a Roaring Rampage of Revenge.