Some fandoms [[FriendlyFandoms just mesh well]]. The timelines and continuities can be made to fit without much difficulty, they might have similar premises or ideologies, and they have characters that you just know would love (or hate) to meet each other. The chances of having them cross over increase if they're made by the same company, written by the same author, and/or have similar character designs.

Some fandoms [[ObviousCrossoverMethod are so accessible]] that they're crossed with just about everything else.

Related to FandomSpecificPlot. A common form is the DoppelgangerCrossover. Contrast the WeirdCrossover.
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!!Examples:

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%%* Advertising/SegataSanshiro and everything else, nuff said.
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[[folder:Anime & Manga]]
* ''Franchise/SailorMoon'':
** The large number of ''Anime/SailorMoon'' crossovers with ''Anime/MobileSuitGundamWing'', which typically pair the Senshi and the Gundam Pilots romantically. This is presumably because ''Wing'', by way of its {{Bishonen}} male cast, served as a GatewaySeries to get girls into the HumongousMecha genre, and the fact that both of them aired on Cartoon Network's Creator/{{Toonami}} block around the same time. This could explain why there are so many ''Anime/SailorMoon''/''Anime/DragonBallZ'' crossovers as well.
** ''Anime/SailorMoon'' and ''Anime/YuYuHakusho'' has also been a very popular crossover, on the basis that the authors of both series are married to each other.
* ''Manga/FullmetalAlchemist''/''Franchise/HarryPotter''. For no real reasons other than that both have involved the Philosopher's Stone and take place in fantastic versions of European countries. In the [[Anime/FullmetalAlchemist2003 anime]]/[[Anime/FullmetalAlchemistTheConquerorOfShamballa movie]] Ed even [[FanficFuel travels to]] an AlternateUniverse, which could [[FandomSpecificPlot easily be changed to the HP one]].
* As of this writing, ''Manga/{{Naruto}}'' has over 11,200 cross-over stories in its crossover section on FF.net, plus however many in the main section. ''Naruto'' fits just about anywhere, apparently.
** With ''Manga/{{Bleach}}'', because [[{{Shounen}} they have the same audience]].
** With ''Manga/OnePiece'', if only for the [[CoolVersusAwesome Ninjas vs. Pirates.]]
** With ''WesternAnimation/TeenTitans2003'', mostly because of Raven/Naruto, two people with pasts involving demons. It helps that ''Teen Titans'' ends with Raven unattached.
** With ''Literature/HarryPotter''. Bringing in the characters as transfer students is more than just popular, but numerous stories where Harry discovers he's an Uchiha/Hatake/insert-bishie-indicating-surname-here (or is raised as a member of that family). Team Seven (or just Kakashi) also seems to get themselves hired out as long-term bodyguards often enough for Tsunade to pay off every single gambling debt she's ever had, plus interest.
*** It's worth noting that even among the more serious stories here, the two universes have plenty of common similarities - a singled-out ChosenOne, a snake-themed villain with an obsession for immortality, a school of special arts, a group of three young heroes the same age ([[TwoGuysAndAGirl two boys, one girl]]), a long-running MythArc, large cast...
* ''Manga/TsubasaReservoirChronicle'' is effectively the anime/manga version of ''Doctor Who'', due to its premise allowing characters to travel between different universes.
* ''Manga/InuYasha'' and ''Manga/YuYuHakusho'', seeing how they both deal with demons, and separation of worlds makes a good explanation of why youkai seemingly no longer exist in the modern era.
* ''Anime/NeonGenesisEvangelion'' crosses over with the ''Franchise/CthulhuMythos'' a lot. Besides fanfics there are even [[TabletopGame/CthulhuTech tabletop games]] whose premise is mostly Eva plus Cthulhu. Both are very bleak, highly psychological, symbolism and mysticism-filled, [[CosmicHorrorStory Cosmic Horror Stories]] about man's arrogance and place in the universe. Eva focuses a bit more on the human, psychological side while Lovecraft on the incomprehensible monster side and so writers like the mesh the two.
* A lot of people have made fanvids of ''Manga/{{Trigun}}'' to ''Series/{{Firefly}}'''s theme song.
* ''Franchise/{{Digimon}}'' and ''Franchise/{{Pokemon}}'' are incredibly common crossover stories, most of the time with each other, but crossovers with other series aren't uncommon.
** Since Beat's birthday in ''VideoGame/TheWorldEndsWithYou'' is the same day as [[PopCultureHoliday Odaiba Memorial Day]], a surprising amount of people draw Beat with Digimon on that day.
* The Doctor being an alien, time traveler, psychic, ''and'' cross-dimensional traveler with the preferred alias of "John Smith" makes ''Series/DoctorWho'' hard to resist for ''Literature/HaruhiSuzumiya'' crossover fanfic writers.
* Crossovers between ''Anime/CodeGeass'' and ''Anime/MobileSuitGundam00'' are also common. [[spoiler: Perhaps it's because of that EnemyMine plan that both Lelouch and Celestial Being employ]]. Creator/BandaiNamcoEntertainment made it official when both series debuted alongside each other in the ''[[VideoGame/SuperRobotWarsZ Second Super Robot Wars Z]]''.
** Not to mention ''Anime/CodeGeass'' and ''Manga/DeathNote'', mostly due to both shows having {{Villain Protagonist}}s who are {{Magnificent Bastard}}s, have a following (one's a rebellion, the other's a cult), have powers involving death (not really, but Lelouch's most memorable use with his Geass would be his first command, which was simply "Die!"), and have secret identities.
* Fans of ''Anime/PuellaMagiMadokaMagica'' tend to also like Creator/UmeAoki's other works, ''Manga/HidamariSketch'', which is more conventionally {{Moe}}. Considering what [[CosmicHorrorStory kind of story]] PMMM is, the adjoining of those two is [[SuperDeformed widely]] disturbing. Clearly this has been noted by the producers; a commercial for the ''Puella Magi Madoka Magica'' Movie appeared in the first episode of the fourth season of the ''Hidamari Sketch'' anime, aired early October 2012. This is hardly coincidental, as producers purchase the entire OtakuOClock block and has a free rein on what commercials to put on.
** For every fandom, there are a few fics that crossover with this anime. They're usually about the main cast of said fandom becoming Madoka-styled magical girls/boys.
* ''Anime/PrettyCure'':
** The franchise has its fair share of these, often overlapping with DoppelgangerCrossover. The most common seem to be with {{Tokusatsu}} shows (in particular ''Franchise/SuperSentai'' and ''Franchise/KamenRider'', since the three shows air in the same block) and with the ''Franchise/{{Gundam}}'' franchise. Other popular crossovers are with ''Manga/SailorMoon'', ''Anime/PuellaMagiMadokaMagica'' (as of 2011) and ''Anime/SaintSeiyaOmega'' (as of 2012, especially concerning ''Heartcatch'', since both shows [[hottip:*:at least, the first season of Omega]] had Yoshihiko Umakoshi as character designer).
** ''Anime/MahoGirlsPrecure'': While most ''Anime/PrettyCure'' entries are commonly crossed with other Tokusatsu shows, ''Maho Girls'' is usually paired with ''Series/KamenRiderWizard'' and ''Series/MahouSentaiMagiranger'' due to similar themes, until it garnered a Pixiv tag titled "[[http://tinyurl.com/zyejnzg Nichi Asa Majutsu Kyoukai]]", translated as "Sunday Morning Magic Association."
* ''TabletopGame/YuGiOh'': In pixiv fanart, Zoodiac monsters are often seen with ''Anime/KemonoFriends'' because of their similar aesthetics. Here's a [[https://www.pixiv.net/member_illust.php?mode=medium&illust_id=62364097 fanart]] treating Serval as a member of the Archetype.
* ''Anime/YukiYunaIsAHero'' and ''Anime/PuellaMagiMadokaMagica'' have many similarities and many differences. Fans have enjoyed crossing them over, especially when it comes to Togo and Homura meeting.
* ''Franchise/LyricalNanoha'' and ''Anime/PuellaMagiMadokaMagica'' are two popular DarkerAndEdgier magical girl series that commonly get crossed over.
* {{Sports Stor|y}}ies are often crossed with each other due to their mundane high school (or sometimes college) setting and shared audience. Common examples are ''Manga/{{Haikyuu}}'', ''Anime/YuriOnIce'', ''Anime/{{Free}}'' and the Creator/ProductionIG version of ''Literature/RunWithTheWind''. The latter is sometimes crossed with ''Manga/{{Haikyuu}}'' because of the ''MemeticMutation'' of calling Kakeru the running version of Kageyama. [[https://archiveofourown.org/works/16705096 Some]] [[https://archiveofourown.org/works/16591649 Fanfics]] depict them as being related in some way.
* Many fan-works revolve around the basketball teams from ''Manga/SlamDunk'' and ''Manga/KurokosBasketball'' playing against one another.
[[/folder]]

[[folder:Comic Books]]
* ''Franchise/{{Batman}}'' with ''WesternAnimation/MiraculousLadybug'' is a surprisingly common trend. A lot of it stems from the Fanfic/MaribatAU, which began the trend of [[CrossoverShip shipping Marinette with Damian]]; other Marinette/Bat-Boy ships are also starting to become popular. In an alternate trend, sometimes Bruce is revealed to be Marinette's biological father.
[[/folder]]

[[folder:Film -- Animated]]
* ''Franchise/{{Frozen}}'':
** There is a ''ridiculous'' amount of ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' FanArt crossed over or mashed up with ''Frozen''. The MLP fandom saw parallels with Elsa's uncontrolled powers nearly causing her to [[AboveGoodAndEvil abandon morality and society]] and Anna's attempt to rescue her from it with the backstory of Celestia and Luna (where Luna's jealousy caused her to attack Celestia and be exiled to the moon) and latched on hard. Elsa is drawn as a Unicorn or Alicorn, and Anna is usually drawn as an Earth Pony.
** ''Frozen'' and ''WesternAnimation/{{Tangled}}'' thanks to Eugene and Rapunzel having a split second cameo in ''Frozen''.
** Elsa has ice powers, as do Jack from ''WesternAnimation/RiseOfTheGuardians'' and Periwinkle from ''Franchise/DisneyFairies'', so many fans crossover (and ship) the characters.
* ''WesternAnimation/TheNightmareBeforeChristmas'' and ''WesternAnimation/CorpseBride'' are often crossed over because Creator/TimBurton wrote them. The events of ''Nightmare'' will have happened, despite the fact that the events of ''Nightmare'' takes place in 1993, the year the movie came out, and ''WesternAnimation/CorpseBride'' takes place somewhere in the Victorian Era.
* The Buzz/Jessie ship from the ''Franchise/ToyStory'' series inspired a flood of fanart crossovers with the SpaceWestern ''Series/{{Firefly}}''.
* ''WesternAnimation/{{Brave}}'', ''Franchise/HowToTrainYourDragon'', ''WesternAnimation/{{Tangled}}'', and ''WesternAnimation/RiseOfTheGuardians'' took FriendlyFandoms to a new level and became a fandom of its own, ''Fanfic/RiseOfTheBraveTangledDragons''. They are often sent to [[Literature/HarryPotter Hogwarts]] or the [[WesternAnimation/AvatarTheLastAirbender Avatar world]].
* ''Franchise/DisneyFairies'' with ''WesternAnimation/StrangeMagic'' thanks to both starring fairies.
* There are countless crossovers and {{Crossover Ship}}s between Franchise/DisneyAnimatedCanon and just about every popular Disney-inspired animated film. ''WesternAnimation/ThePrinceOfEgypt'', ''WesternAnimation/TheSwanPrincess'', and ''WesternAnimation/{{Anastasia}}'' are popular examples.
* Creator/{{Disney}}'s ''Franchise/LiloAndStitch'' and Creator/DreamWorksAnimation's ''Franchise/HowToTrainYourDragon'' franchises receive a ton of crossover fan art (especially of Stitch and Toothless) for not only featuring unique, misunderstood human beings who bond with strange, powerful, yet oddly adorable creatures, but also because their [[WesternAnimation/LiloAndStitch original]] [[WesternAnimation/HowToTrainYourDragon2010 films]] share the same directors and writers in Creator/ChrisSanders (who created and voiced Stitch and practically self-plagiarized a bit for his design of the Night Fury Toothless) and Creator/DeanDeBlois (who would also write and direct ''HTTYD''[='=]s [[WesternAnimation/HowToTrainYourDragon2 sequel]] [[WesternAnimation/HowToTrainYourDragonTheHiddenWorld films]]).
* ''WesternAnimation/TurningRed'' with ''WesternAnimation/{{Encanto}}'' thanks to both being Disney animated films involving families with magical abilities dealing with GenerationalTrauma.
[[/folder]]

[[folder:Film -- Live Action]]
* ''Harry Potter'' meets ''Franchise/StarWars'' quite often as well. Both involve singled-out main characters separated from everyone else by supernatural affinity, with a tight clique of close friends leading a resistance against a villain related to the hero in some way, both series use similar tropes and myth arcs, and The Force makes a handy explanation of ''Potter'' magic. It takes quite a bit of explaining to work the two together, however.
* The ''[[Film/TheAvengers2012 Avengers]]'' crossover pile is growing at a near-exponential rate, closing in on second place in the films category for crossovers on fanfiction.net. It also helps that [[Franchise/MarvelCinematicUniverse the world]] has a lot of fleshing out to do and a lot of potential in terms of crossing over, often with traditional Marvel properties like Spider-Man (which became movie canon in 2016) and the X-Men.
* This is common within the horror genre, where stories are constantly filled with shout-outs that leave writers with plenty of FanficFuel. Some crossovers that eventually grew popular enough to become canon in their own right include ''Franchise/AlienVsPredator'' ([[Franchise/{{Alien}} evil]] [[Franchise/{{Predator}} aliens]] that both featured in badass '80s action/horror flicks), ''Film/FreddyVsJason'' ([[Franchise/ANightmareOnElmStreet two of the most]] [[Franchise/FridayThe13th iconic villains]] of '80s {{slasher movie}}s), and the [[Franchise/UniversalHorror Universal monsters]] as a whole (classic '30s and '40s horror films made by [[Creator/{{Universal}} the same studio]], in one of Hollywood's first examples of a [[ModularFranchise shared movie universe]]).
* ''Franchise/{{Godzilla}}'', ''Film/{{Gamera}}'', and ''[[Franchise/UltraSeries Ultraman]]'', thanks to the shared love of {{Kaiju}}. Usually, it's having their characters fight each other, but sometimes they have heroic teamups. Expect to see ''Film/PacificRim'' sometimes as well.
** This reaches the logical conclusion with the ''Amalgam'Verse'', as shown in the fanfics ''Fanfic/TheBridge'' and ''Fanfic/GodzillaNewEra''- nearly every kaiju story ''ever'', from the aforementioned Godzilla, Gamera, Ultra Series, and Pacific Rim, straight through to Film/{{Cloverfield}}, Film/{{Gorgo}}, and even numerous American 50s giant monster movies, have been fused into a single world, using the Heisei Godzilla series as the base and building from there. Though at first it existed only to provide background for ''The Bridge'', [[WeirdCrossover a crossover with My Little Pony]], it has since been expanded on via ''New Era'' and the series of short stories called ''Tales of the Amalgam'Verse''. Here's [[https://docs.google.com/document/d/1GVqMklzy9mIKS057nsZje3dOgWOQ-HS6i8c1SByluzA/edit the full reading list]] [[https://docs.google.com/document/d/1U8ETC0xSbH33BQ94cHQR7_l1kU8ipiEYRkL8v-wX0IE/edit?usp=sharing and the roster for the spinoff Humanity’s Stand, which covers most of the main kaiju players currently on Earth.]] Regrettably, an up-to-date roster for the entire FanVerse is not currently available. [[note]] The main kaiju [=PoVs=] in The Bridge are Godzilla, Mothra, Anguirus, Rodan, Destroyah, Xenilla, Monster X, Gigan, Megalon, and an albino gyaos later called Irys. The main kaiju [=PoVs=] of Humanity’s Stand (so far) seem to be Gamera, Zilla Jr, Krystalak, Manda, Kong, Kiryu, and Gabara, with Miki Saegusa, Akane Yashiro, and Stacker Pentecost as human [=PoVs=]. Some of the tie-in short stories and other fics include the [=PoVs=] of Raiga, Biollante, Gomora, and Ultraman Belial, to name a few.[[/note]]
[[/folder]]

[[folder:Literature]]
* It's not so much that it ''does'' mesh well with everything as that everyone and their cat has heard of it, but ''Literature/HarryPotter'' has been crossed over with nearly everything. There's one ''Harry Potter''/''Disney's WesternAnimation/{{Aladdin}}'' crossover, completely disregarding the huge time difference and the not exactly ''friendly'' attitude Agrabah would have towards wizards once it was not only a Muslim city, but a Muslim city that has "getting hugely screwed over by a sorcerer" in its recent history.
** The Veil of Death from the Department of Mysteries is sometimes also used as a link to the [[Manga/FullmetalAlchemist Gate of Truth]], and as well-written stories such as ''[[http://www.fanfiction.net/s/6436196/1/Penance Penance]]'' can attest, it can work to a strong degree.
** ''Harry Potter''/''Literature/TheTwilightSaga'', naturally. Someone in the story will usually comment on [[ActorAllusion how much Edward Cullen looks like Cedric Diggory]] if they aren't [[DoppelgangerCrossover revealed to be the same person]].
** ''Series/WizardsOfWaverlyPlace'', ''Film/PercyJacksonAndTheOlympians'', and ''Literature/ArtemisFowl'' also cross over frequently due to similar premise, similar themes and similar locations. It helps that the ''Percy Jackson'' universe is pretty easy to justify--"Harry Potter, son of insert-god-here" is a popular path.
* ''Literature/MaximumRide'' and ''Literature/TheTwilightSaga'' seem to get crossed over quite a lot for such an odd combination.
* The Franchise/CthulhuMythos fits well with anything vaguely fantasy, horror, sci-fi, or mystery, from ''Literature/SherlockHolmes'' to ''TabletopGame/DungeonsAndDragons'' to the Franchise/MarvelUniverse. Hence ''TabletopGame/CthulhuTech''. There was even a ''Franchise/{{Batman}}'' Elseworld that revolved around Arkham Asylum crossed over with the Cthulhu Mythos, making it a professional version of this trope.
** The IDW comic book series ''Infestation 2'' sets Lovecraftian threats against characters from ''ComicBook/TheTransformersIDW'', ''TabletopGame/{{Eberron}}'', ''[[ComicBook/TeenageMutantNinjaTurtlesIDW Teenage Mutant Ninja Turtles]]'', ''Franchise/GIJoe'', and ''ComicBook/ThirtyDaysOfNight''.
* ''Literature/GoodOmens'' is a natural crossover with ''Series/{{Supernatural}}'', seeing as SPN's demon Crowley was modeled after ''Good Omens''' demon Crowley, so there's a lot of meshing of their respective apocalypse/heaven-and-hell/demons-and-angels plots. It's also a natural crossover with with ''Series/Lucifer2016'', another series that has a NobleDemon protagonist who's fond of humanity despite his infernal roots.
* ''Literature/TheMortalInstruments'' and ''Literature/TheInfernalDevices'' don't have a huge crossover file yet, but it's steadily building. Considering the fact that ''The Infernal Devices'' is really just a prequel and many characters are either ancestors of characters in ''The Mortal Instruments'' or present in both series (such as Magnus Bane and various vampires), it's not surprising.
* ''Literature/PercyJacksonAndTheOlympians'' (and ''Literature/TheHeroesOfOlympus'', naturally) have major crossover fuel with ''Franchise/{{Pokemon}}'' and ''Literature/TheKaneChronicles''. Of course, the latter is in [[TheVerse the same universe]] anyway, as is ''Literature/MagnusChaseAndTheGodsOfAsgard''.
* ''{{Literature/Animorphs}}'' and ''Literature/MaximumRide''. People love to have the Flock meet Tobias, since they're both bird/human.
* ''Literature/LandOfOz'', ''Literature/PeterPan'', and ''Literature/AlicesAdventuresInWonderland'' due to their similarly whimsical feels. As both the ''Land of Oz'' and ''Alice's Adventures In Wonderland'' series are in the public domain, there are even for-profit works which cross them over.
* ''Literature/WarriorCats'':
** If a work stars cats then it's likely been crossed over with ''Warriors''.
** ''Warriors'' and ''Literature/WatershipDown'' has crossed over due to FriendlyFandoms. It also adds a new layer to the stories because one stars cats and the other stars rabbits.
* ''Literature/{{Worm}}'' and ''WebAnimation/{{RWBY}}'' have a surprising number of crossovers. At time of writing, fanfiction.net lists more Worm/RWBY crossovers than ''Worm''/''Manga/MyHeroAcademia'' crossovers, despite the latter work having significantly more in common with the former (e.g. superheroes). Only four other franchises have more Worm crossovers than RWBY[[labelnote:*]]In descending order: Fate/Stay Night, Harry Potter, Naruto, and Warhammer[[/labelnote]], all of which are significantly more well-known than RWBY.
[[/folder]]

[[folder:Live-Action TV]]
* ''Series/{{House}}'' FanFic is famous for its crossovers. Notable ones are ''Franchise/{{Batman}}'', ''Series/{{Angel}}'', ''Series/{{Bones}}'', and ''Series/DoctorWho''. There are also a few with ''Series/{{Firefly}}'', including one with River (where she really sparks his curiosity due to how strange her case is; it's never explained how she got there). It's not uncommon to find a crossover between ''House'' and ''Series/{{Blackadder}}'', either, considering that the latter also stars Hugh Laurie, though in a [[UpperClassTwit complete]] [[TheDitz 180]] from his role in ''House''.
* There is a [=LiveJournal=] community specifically for crossovers between ''Series/{{Heroes}}'' and ''Series/{{Supernatural}}''. The fandoms overlap because if you want broslash, you're pretty much going to have to be a fan of at least one of them.
* There is also quite a few crossovers between ''Series/{{Supernatural}}'' and ''Series/Numb3rs'', as both shows are about brothers that work together.
* ''Series/{{Smallville}}''/''Franchise/{{Batman}}'', especially Bruce/Lex and/or Bruce/Clark. Of course, the fact that there ''were'' plans to bring a young Bruce[[note]](Adam Knight)[[/note]] to the town helps matters a bit. Plus, the show [[WhatCouldHaveBeen was originally going to be about young Bruce]].
* Franchise/{{Buffyverse}}:
** In general, if a show, movie, book, or game has a young ActionGirl protagonist, it’s probably just a matter of time before somebody writes a fix about her finding out she’s the new [[TheChosenOne Slayer]].
** ''Series/{{Firefly}}'' is a big one, due to both shows being created by Creator/JossWhedon. From ''Series/BuffyTheVampireSlayer'', Xander (or, less frequently, Willow or Dawn) gets sucked into a portal, dimensional rift, etc., and ends up aboard the ''Serenity''. Alternatively, [[MysteriousWaif River Tam]] is a Slayer, with the Academy as a corrupted Watchers Council. One fan attempt at CanonWelding between the two universes, called the [[https://screenrant.com/whedonverse-universal-slayer-theory-angel-buffy-firefly-dollhouse/amp/ “Universal Slayer Theory”,]] even treats the latter setup as {{fanon}} while also tying in other Whedon works.
** ''Series/StargateSG1'' crossovers are so ubiquitous in the ''Buffy'' fandom that in many cases they're not even labeled as crossovers unless they cross with a ''third'' fandom. There's a ''Franchise/{{Halo}}''/''Buffy''/''SG-1'' fic where Xander goes as John-117 on Halloween (the timeline problems there are never addressed) and things change... a lot. It's good if you can ignore the timeline problems. Oh, and Xander actually remembers Jessie and actually still has his death as a source of grief.
** ''Series/DoctorWho'' is such a common crossover that fans can easily start mixing canon from both in their minds. Both expanded universes have had brief crossovers from the other universe -- an Eighth Doctor novel has a cameo from Spike, and the Tenth Doctor and Rose make a cameo appearance in ''Buffy'' season 8.
** Another one is with ''{{Series/Merlin|2008}}'', due to Creator/AnthonyHead being a major player in both series. It usually involves Buffy getting transported back to Camelot somehow, but a few other variations exist as well.
** ''{{Series/Angel}}'' and ''Buffy'' get crossed with ''{{Series/Bones}}'' a lot because Creator/DavidBoreanaz’s characters are quite similar in some ways. The theory of Booth being Angel’s Shanshu, or reward of becoming human, has quite a few fans.
* ''Series/{{Battlestar Galactica|2003}}'' eventually gets crossed with any running Sci-Fi due to the LostColony premise. For instance, the refugee fleet entering ''Franchise/StarTrek's'' [[TheFederation United Federation of Planets]], with the resulting political fallout and attacks by the Cylons, is a common idea.
** In particular, fics crossing over ''Galactica'' with the Franchise/StargateVerse are common as mud, perhaps because ''SG-1'', ''Atlantis'' and ''BSG'' all used to air on Creator/{{Syfy}} on the same night originally. Such fics will usually have the following features and plot points, almost certainly due to a massive upsurge of FollowTheLeader after ''Fanfic/ReunionsAreABitch'' pioneered them:
### The Cylon attack that kicked off the events of the series either never happened, or went drastically the reverse of how it happened in canon, with the Colonials winning.
### The Colonials are/become a militaristic regime, bent on conquest.
### Said conquest includes conquering their "rogue" thirteenth colony, Earth.
### The Colonials completely underestimate how much [[CurbStompBattle curb-stomping]] a couple of Prometheus-class ships equipped with Asgard weaponry can dish out.
** Strangely, the number of crossovers between the [[Series/BattlestarGalactica1978 original '70s version]] of ''Galactica'' and ''Franchise/StarWars'' can probably be counted on one hand, even though the former was very heavily influenced by the latter.
* A crossover of yesteryear: ''Series/{{Highlander}}'' and ''Series/ForeverKnight''. There are a ''lot'' of those.
* ''Series/DoctorWho'' [[LauncherOfAThousandShips has a face that's 'launched a thousand ships']]. Travel through time and space tends to facilitate crossovers with anything not too [[SlidingScaleOfSillinessVersusSeriousness cartoonishly illogi-]] [[CrackFic oh, who are we kidding?]]
** ''Series/KamenRiderDecade'' is effectively the Toku/Japanese version of this.
** ''Series/QuantumLeap'' is effectively the American version of this, as well. Double points that it's perfect for writing a FixFic.
* ''Series/{{Supernatural}}'' actually gets crossed with a lot of stuff, but most often with ''Series/{{Smallville}}'' (which almost ''always'' includes Dean/Chloe, though there's an occasional Sam/Chloe or Dean/Lois fic out there[[note]]perhaps even [[CastingGag Dean/Lana]][[/note]]) and ''Series/BuffyTheVampireSlayer'' (almost ''always'' including Dean/Buffy, Dean/Faith, or Sam/Faith, though some Sam/Willow, Spike/Dean, Angel/Dean, and/or Spike/Dean/Sam fics show up sometimes). The number of crossovers with ''Series/DoctorWho'', ''Series/{{Torchwood}}'', and ''Series/{{Heroes}}'' are growing rather quickly. Crossing with ''Series/DarkAngel'' is also common, as Dean shares the same actor (Creator/JensenAckles) as the identical twins Ben and Alec, and since the latter two are [[GeneticEngineeringIsTheNewNuke genetically engineered]] and [[ClonesArePeopleToo clones]], it's an ObviousCrossoverMethod to say Dean is the person they were cloned from.
** Superwho (''Supernatural'' crossed over with ''Doctor Who'') has almost a fandom of its own. Apparently the writers of ''Supernatural'' caught wind of this, since they named a new character "Amy Pond".
*** It can be considered a DoppelgangerCrossover: Mark Sheppard played both Crowley in Supernatural and Canton in ''Doctor Who''.
** Superwholock (''Series/{{Supernatural}}'' crossed with ''Series/DoctorWho'' crossed with ''Series/{{Sherlock}}'') has become increasingly popular, uniting Wholock (see below) and Superwho in one all-encompassing fandom.
*** And to this can be added Superwhoavengerlock, which is what you get when you add ''The Avengers''.
*** ''Series/{{Merlin|2008}}'' and ''Literature/HarryPotter'' may or may not come along for the ride.
*** It's no surprise that ''Series/TeenWolf'' has been enthusiastically and seamlessly crossed with ''Supernatural'', but it remains to be seen if it will join the Superwholock party.
** There's a decent amount of crossover with PoliceProcedural shows like ''Series/{{NCIS}}'' and ''Series/CriminalMinds'', mostly due to the recurring Winchester brothers chased by the FBI subplot.
* In general, different UrbanFantasy and present-day SciFi (think Sg-1 or Doctor Who) universes tend to mix well as they all share many common themes - TheMasquerade, OurMonstersAreDifferent, FantasyKitchenSink, LikeRealityUnlessNoted as well as a generally darker and more cynical tone. Writers like the challenge of mixing and combining different universes as well as bouncing the usually [[DeadpanSnarker snarky]], [[KnightInSourArmor cynical]] yet [[ChronicHeroSyndrome undoubtedly]] [[AntiHero heroic]] characters against each other.
* For some reason, ''Series/{{Sherlock}}'' and ''Literature/GoodOmens'' crossovers are quite popular. It could have something to do with the fact that the most popular pairing in each fandom (Sherlock/John and Crowley/Aziraphale, respectively) have parallels, making this a rare case of cross-fandom ShipMates. It doesn't hurt that both stories take place in Britain.
* The shows in the Franchise/DisneyChannelLiveActionUniverse and Series/NickVerse since the rise of online fandom are crossed over constantly regardless, as they are all set in the same rough time period and genre (KidCom) and most people in their target age groups watch multiples of them and thus have the knowledge to use all the characters in cross-overs:
** ''Series/ICarly'', ''Series/DrakeAndJosh'', ''Series/{{Victorious}}'' and ''Series/{{Zoey101}}'' have many crossovers, because of their shared universe. Nevel/Megan, Freddie/Cat, Sam/Jade are some popular crossover pairings. The four shows ''have'' crossed over in canon as well. In the iCarly episode "iStart a Fan War," [[Series/DrakeAndJosh Craig, Eric, Gavon]], and [[Series/{{Zoey101}} Stacey]] all attend the iCarly fan panel. In ''Victorious'', Helen from ''Drake and Josh'' is the new principal at Hollywood Arts, and there is the "iParty With Victorious" crossover with ''iCarly''. There are also two more shows in the works that will join this set, with ''Series/SamAndCat'' being a ''crossover SpinOff'' with Cat Valentine from ''Victorious'' and Sam Puckett from ''iCarly'', as well as a SpinOff with the character Gibby from ''iCarly''.
** ''Film/CampRock'' is a very popular crossover for ''Series/HannahMontana'', ''Series/WizardsOfWaverlyPlace'' and some with ''Series/SonnyWithAChance''/''Series/SoRandom''
* ''Series/{{Heroes}}'' and ''Series/{{Lost}}'' get crossed over a lot thanks to their overlapping fanbases and similar styles.
* ''Series/{{Supernatural}}'' and ''Series/{{Lost}}'' get crossed over a lot for some unfathomable reason. Occasionally it's a DoppelgangerCrossover due to Creator/MarkPellegrino and Creator/TitusWelliver appearing in both, but that doesn't account for even half of the fic out there.
* ''Franchise/StarTrek[=/=]Franchise/StarWars'' crossovers are pretty common; not only are they the two biggest science fiction franchises, but nerds often write them as a side effect of arguments over which side's ships are more powerful.
* ''Series/{{NCIS}}'' and ''Series/CriminalMinds'' tend to get crossed over with each other a lot. It even shows with [[http://www.fanfiction.net/crossovers/NCIS/1668/# the NCIS crossover page]] and [[http://www.fanfiction.net/crossovers/Criminal_Minds/2362/# the Criminal Minds crossover page]]. Sort either page by popularity makes this abundantly clear.
* ''Series/{{Castle|2009}}'' and ''Series/{{Bones}}'' seem to be crossed over a fair bit. There's also more than a few crossovers with ''Series/{{Firefly}}'' that tend to suggest some kind of connection between Richard Castle and Malcolm Reynolds (although the sheer amount of {{Actor Allusion}}s ''Series/{{Castle|2009}}'' makes to ''Series/{{Firefly}}'' help this along).
* If they're not crossing their Disney properties with ''Franchise/KingdomHearts'', they'll cross it with ''Series/OnceUponATime'' (if they're not crossing those two with each other to begin with). For even more fun, the writers have pretty much out and established that it's in the same universe as ''{{Series/Lost}}'' and ''Film/{{Tron}}''. There have also been fanart crossovers with ''Franchise/MassEffect'' due to the same actor playing Kaiden Alenko and Jiminy Cricket.
* ''{{Franchise/Highlander}}'' lends itself to a lot of crossovers, because it's relatively easy to pick a character from another show and make them an immortal. Especially if they're an orphan. It also frequently crosses with ''Series/BuffyTheVampireSlayer'' due to the existence of a Watchers organization in both worlds.
* Because of JustForFun/InspectorSpacetime, ''Series/{{Community}}'' and ''Series/DoctorWho'' fics are getting increasingly common.
* ''Series/AmericanHorrorStory''[='=]s most popular crossover? [[http://www.fanfiction.net/Glee-and-American-Horror-Story-Crossovers/4947/9087/ It's with]] ''Series/{{Glee}}'', of all shows. This is likely due to the fact that both shows were made by the same guy, Ryan Murphy. Quinn/[[TroubledButCute Tate]] is a particularly common pairing for such crossovers.
* ''Series/{{Sanctuary}}'' and ''Series/{{Warehouse 13}}'' match up quite well. They have similar but non-conflicting premises, where ''Sanctuary'' collects fantasy creatures while ''Warehouse 13'' collects fantasy devices, and both of them are private entities secretly supported by governments to contain the Masquerade. They both have flashbacks and important plot events that happened in late 1800s: on ''Warehouse 13'' the change from Warehouse 12 to 13 and Creator/HGWells backstory, and the vampire blood on ''Sanctuary'' and the founding of Sanctuary itself.) There's even a shared HistoricalDomainCharacter, UsefulNotes/NikolaTesla, who is still alive on ''Sanctuary'' and helped build ''Warehouse 13''. Sadly, neither of these properties is very fanficed, and thus crossovers sparse.
* The ''Series/{{Daredevil 2015}}'' Netflix series has a lot of fix about Matt and Comicbook/{{Hawkeye}} falling into the same dumpster, which often segway into discussions about how one is blind and one is deaf.
* ''Series/TheWalkingDead'' frequently gets crossed over with, of all things, the cult action film ''Film/TheBoondockSaints'', on account of both starring Creator/NormanReedus as a badass AntiHero.
* ''Series/TheSentinel'' gets crossed with a variety of other series. It makes may be a standard crossover of "The cast of the Sentinel meet X" or the Sentinel/Guide concept may be used for a FusionFic.
* At least three shows have done an "[[Series/TheApprentice Alan Sugar]] pitches on ''Series/DragonsDen''" sketch: ''Series/DeadRingers'', ''Series/HarryAndPaul'', and a SelfParody by the original shows for Comic Relief.
[[/folder]]

[[folder:Tabletop Games]]
* ''TabletopGame/Warhammer40000'' and ''Anime/NeonGenesisEvangelion''. Hell, ''Warhammer 40000'' has probably been crossed over with pretty much everything by now.
** You could have any fictional setting just be an undiscovered world or sector of the galaxy, and any magic can simply be [[HandWave handwaved]] away as "Warp sorcery."
** ''TabletopGame/Warhammer40000'' and ''Franchise/MassEffect'' do well together. Of note are ''[[http://z6.invisionfree.com/bljunkies/index.php?showtopic=1260 Hammerhand]]'' and ''[[http://www.fanfiction.net/s/6731833/1/Angels_of_the_Storm Angels of the Storm]]''
** Though you wonder that there haven't been more ''40k''[=/=]''Franchise/DragonAge'' crossovers, what with the ridiculously similar magic system and the Qunari (who are Tau, but bigger and grey).
* ''TabletopGame/WarhammerFantasy'' and ''Literature/ASongOfIceAndFire'' / ''Series/GameOfThrones'' do well together, since both are firmly set in TheDungAges where the worst historical abuses of the feudal system are daily life.
* ''TabletopGame/{{Exalted}}'' is often crossed over with ''Literature/{{Worm}}''. (The two universes, despite being very different variations of the fantasy genre, [[BeingGoodSucks share]] [[CrapsackWorld similar]] [[HeWhoFightsMonsters themes]].) Or, [[http://forums.spacebattles.com/threads/why-is-worm-so-popular-here.294794/page-2#post-13927592 to quote Ryuugi:]]
--> Imagine a setting in which enormously powerful super-weapons called 'Shards' attach themselves to humans in extraordinary situations, giving them the power to change the world to their will, but painting their emotional highs and lows in broader strokes. The sources of these shards are tremendously powerful superbeings, one of which is a shining golden man.
--> What setting am I talking about?
* A variation of this can be seen within ''TabletopGame/DungeonsAndDragons'' with adapting specific adventures to settings they weren't originally intended for and few combinations have become pretty common among the Dungeon Masters.
** Third Edition campaign ''TabletopGame/RedHandOfDoom'' and Fifth Edition ''TabletopGame/TyrannyOfDragons'' are often placed in the ''TabletopGame/{{Dragonlance}}'' universe, due to the fact that the BigBad of that setting, dragon queen Takhisis, is a blatant {{Expy}} of the BigBad of the two modules, dragon godess Tiamat.
** ''Magazine/{{Dungeon}}'' Magazine's final campaign, ''TabletopGame/SavageTide'' features a whole part on the famous Isle of Dread. As such it is very common to adapt it to ''TabletopGame/{{Mystara}}'', where Isle of Dread was originally placed.
[[/folder]]

[[folder:Video Games]]
* ''Franchise/{{Halo}}'':
** With ''Franchise/MassEffect''. Both are [[ScienceFiction sci-fi]] videogames with badass SpaceMarines killing aliens and saving Humanity from extinction.
** It is not uncommon for ''Franchise/{{Metroid}}'' to be meshed together with it, due to common traits shared by Samus and Master Chief, as well as the overall atmosphere of both series. [[CrossoverShip Fans having a habit of pairing up the main protagonists]] and the existence of ''WebAnimation/{{Haloid}}'' might also have something to do with it.
** Because they may be in the same continuity, ''WebAnimation/RedVsBlue'' crossovers are pretty common.
* ''Franchise/KingdomHearts'':
** With just about anything, really. It helps that ''Kingdom Hearts'' is itself a crossover between Disney and Square-Enix, and the entire premise of the game is that the heroes go from one Disney world to another to help fight off outside interference. How much any given fanfic keeps the worlds separate in this fashion varies, especially if there's [[MassiveMultiplayerCrossover more than one world involved]].
** With ''VideoGame/TheWorldEndsWithYou'' characters canonically existing in the ''KH'' verse as of ''[[VideoGame/KingdomHearts3DDreamDropDistance 3D]]'' and Disney owning both Marvel and the rights to the ''Star Wars'' franchise, the possibilities (even without the six degrees principle) are endless.
* ''VideoGame/TalesOfVesperia'' and ''Franchise/BlazBlue''. At least according to the author of the fanfic. Though it's in the Tales of section rather than the Crossover section.
* The huge cast in ''Franchise/TouhouProject'' means you can get a bunch of obvious crossovers. Or as some say: "Rule ⑨: If it exists, there is a Touhou version of it". Also, Rule P: If it exists, it has been "ponified" (that is, the characters are drawn as ponies from ''WesternAnimation/MyLittlePonyFriendshipIsMagic''). It overlapped with Rule ⑨ once.
* ''Franchise/SonicTheHedgehog'':
** ''VideoGame/{{Klonoa}}'' gets crossed over with it quite a lot. This is probably helped by (and possibly due to) the fact that Klonoa looks an awful lot like a ''Sonic'' character.
** With ''Franchise/SuperMarioBros''. The fact that it [[VideoGame/MarioAndSonicAtTheOlympicGames happened in canon]] probably helps, but people were doing it for years beforehand.
* ''Franchise/SilentHill'' is one popular resort town. The [[VideoGame/SilentHill2 second game]] in particular popularized the idea of the town being a sentient EldritchLocation that lures sinners to their own personalized hell, creating an easy route for crossover plots: have a character (especially a villain or an AntiHero) get drawn to Silent Hill and battle monsters that serve as metaphorical representations of all the awful things they did.
** As for specific fandoms, crossovers with ''Franchise/{{Resident Evil}}'' can occasionally happen, with both series being famous for their impact on the SurvivalHorror genre, being competitors at the start, and having similarities to each other. It also helps that the Resident Evil characters in particular, can barely catch a break in terms of trauma from the events of the series making them easy candidates to get stuck in Silent Hill, or even helping the other characters out in Silent Hill.
* The entire Japanese HumongousMecha genre, including every SuperRobot and RealRobot show imaginable, largely because of ''VideoGame/SuperRobotWars'' being a professional example of this trope and actively using FixFic commercially.
* ''VideoGame/DevilMayCry'':
** With ''VideoGame/{{Bayonetta}}''. It might or might not be canonically in the same world, but as far as fan fiction is concerned, they are. Common elements include Eva, the mother of Dante and Vergil, being an Umbra Witch who had a pact with Sparda (which is hinted at in one of the item descriptions in ''Bayonetta'') and Madama Butterfly being Sparda's sister (probably because they're both unusually powerful insectoid demons). Look for the villains and anti-heroes of every other ActionGame the writer likes, but especially ''VideoGame/GodOfWar'' and ''VideoGame/{{Darksiders}}''.
** With ''Franchise/ResidentEvil'' many times, partly because ''DMC'' [[DivorcedInstallment started as]] a ''RE'' game before Capcom decided that the mechanics were too different and made it an independent series.
* Crossovers with the ''VideoGame/PaperMario'' series are incredibly common, usually adaptations. Some of the most popular are ''Edventure of the Thousand Year Door'' (combining ''Paper Mario'' with ''WesternAnimation/EdEddNEddy'') and the ''FanFic/PaperMarioX'' series.
* ''VideoGame/KanColle'':
** ''Manga/ArpeggioOfBlueSteel'' overlaps with it ''very'' well, due to their joint reference pools of World War 2-era Imperial Japanese Navy warships and cute girls.
** Kancolle and ''VideoGame/ToukenRanbu'' are commonly crossed over due to being hosted on the same website and having similar premises. The only difference between the two is that while Kancolle focuses on warship girls, ''Touken Ranbu'' focuses on Historical sword boys.
** Other shipgirl games are ripe for a Kancolle crossover, such as the Chinese franchises ''VideoGame/WarshipGirls'' and ''VideoGame/AzurLane''. Even non-anthropomorphic warship games can sometimes be used as crossover fodder, ''VideoGame/WorldOfWarships'' in particular.
* ''VideoGame/ToukenRanbu'' itself. Aside from the aforementioned, this game is frequently crossed over with other works set in historical settings in which the historical figures formerly owning the swords show up, such as ''VideoGame/SengokuBasara'' (to the point where it can be safely assumed "Touken Basara" is the ''most'' popular type of crossover in the [=TouRabu=] fandom ''ever''), ''VisualNovel/{{Hakuouki}}'' or even ''Manga/{{Gintama}}''. There is also a recurring trend to cross over with ''Webcomic/HetaliaAxisPowers'' and ''Manga/HozukisCoolheadedness'' by placing a character from either series (usually Japan from the former and Hōzuki from the latter) as the saniwa. Crossing over with ''VideoGame/Onmyoji2016'' is fairly popular among Chinese fans of this game after it introduces its own sword boy Onigiri (voiced by Creator/KosukeToriumi as the cherry on top).
* ''VideoGame/DarkestDungeon'' and the ''VideoGame/DarkSouls''-''VideoGame/{{Bloodborne}}'' series are all very dark games with strong influence from H.P. Lovecraft, as well as being infamous for their difficulty. There's quite a few fan creation consisting in drawing characters from the Creator/FromSoftware franchises in the style of ''Darkest Dungeon'' (there's also ''Darkest Dungeon'' mods adding characters from those games), as well as gameplay footages from ''Bloodborne'' or a ''Souls'' game edited with lines of ''Darkest Dungeon'' Narrator.
* ''Franchise/{{Metroid}}'' and ''VideoGame/FZero'' see quite a few crossovers due to the protagonists of both being {{Bounty Hunter}}s in science fiction settings.
* ''Franchise/BlazBlue'' and ''WebAnimation/{{RWBY}}'' crossovers are very common due to the ''unbelievable'' amount of [[https://pokesega64.tumblr.com/post/163105916135/pokesega64-red-and-black-clad-travelling similarities]] that both worlds have. A lot more have recently been made thanks to ''VideoGame/BlazBlueCrossTagBattle''.
** Also, ''WebAnimation/{{RWBY}}'' and ''VideoGame/{{Bloodborne}}''. Both are stories about [[HunterOfMonsters Monster Hunters]] with [[MixAndMatchWeapon Mix and Match Weapons]], but with wildly different tones. Consequently, stories about one or more characters from Remnant finding their way into Yharnam to get swept up in the Night of the Hunt are not uncommon. Neither are stories about the Good Hunter, after escaping the Dream, waking up on Remnant.
* ''VideoGame/SuperSmashBros'' is breeding grounds for this, considering that any Nintendo franchise (and whatever else the creators can collaborate with) can be annexed into the Trophy World. Thanks to the World of Light mode in ''VideoGame/SuperSmashBrosUltimate'' and the Spirit system, the possibilities are endless.
* ''VideoGame/{{Ib}}'', ''VideoGame/ForestOfDrizzlingRain'', ''VideoGame/AngelsOfDeath'', and ''Paranormal Syndrome'' are often crossed over together under the "Free(ware) Horror" fan-banner, as all of them are UsefulNotes/RPGMaker games that involve some combination of mysterious young girl and plot-important handsome adult man. ''VideoGame/YumeNikki'', despite not really having an adult man that matches the theme (the closest being how people interpret Seccom Masada-sensei), is included on occasion.
* ''VideoGame/YokaiWatch'' with ''Franchise/{{Pokemon}}'' because they're similar {{mon}} works.
* ''VideoGame/YumeNikki'':
** ''VideoGame/{{Off}}'', due to being offbeat [=RPG=]s with unsettling content.
** ''VideoGame/{{Undertale}}'', as the protagonists are both {{Kid Hero}}es with EyesAlwaysShut in strange lands that can use a knife as a weapon. ''VideoGame/{{Omori}}'' is occasionally added in, despite its protagonist [[spoiler:(initially)]] not fitting the "closed eyes" theme.
[[/folder]]

[[folder:Visual Novels]]
* ''Franchise/AceAttorney'':
** Both this franchise and ''VideoGame/TraumaCenter'' are over-the-top DS games about a relatively ordinary profession. Both are TwentyMinutesIntoTheFuture, and both take place in California (or Japan in the JP versions). Though it's generally agreed they fit well together, crossovers are surprisingly uncommon.
** Goes well with ''VideoGame/EliteBeatAgents'', probably because both are surprisingly well-Americanized DS games featuring {{Large Ham}}s with AnimeHair. Heck, one such crossover is even on the FanficRecs page! ''VideoGame/{{osu}}!'' includes one of such fanfics, to the tune of Music/{{Queen}}'s ''Don't Stop Me Now''.
** [[Creator/{{Capcom}} Unsurprisingly]], there's also a fair amount of art crossing it over with ''VideoGame/GhostTrick''... this is saying something, since ''Ghost Trick'''s fandom is comparatively obscure.
** ''Franchise/{{Danganronpa}}'' is a common target because of the franchises' shared focus on over-the-top trials.
* Any folklore/historical series you can think of has at least one ''Franchise/FateSeries'' crossover, considering the sheer amount of Servants a given character can be paired with.
[[/folder]]

[[folder:Web Comics]]
* You don't have to look far to find ''Webcomic/{{Homestuck}}'' versions of things; in addition to being very popular, it's easy to whip up a [[SailorEarth Sburb session]] for any given fandom, and if you can mimic its distinctive SignatureStyle then that goes a long way.
* ''Webcomic/GirlGenius'' is crossed over incredibly often with ''Webcomic/{{Narbonic}}'', to the point that they’re sometimes not even considered crossovers. This is likely because [[TheSparkOfGenius the spark]] in ''Webcomic/GirlGenius'' is pretty much identical to [[ScienceRelatedMemeticDisorder mad genius]] in ''Webcomic/{{Narbonic}}''.
[[/folder]]

[[folder:WesternAnimation]]
* For some reason, ''Franchise/{{Transformers}}'' tends to get crossed over a lot with ''WesternAnimation/WallE''. Part of it appears to stem from the absurd juxtaposition in settings, no matter which way the crossover goes. ''Transformers'' fans can also appreciate [[http://tfwiki.net/wiki/Bumblebee_%28disambiguation%29 small yellow robots]], especially when it's one who's well-meaning, hard-working, quirky, kind, and generally innocent while also avoiding a "snarky mascot" or TotallyRadical portrayal.
* The [[http://www.fanfiction.net/crossovers/G_I_Joe/717/ FF.net crossover listings for ''G.I. Joe'']] have many stories that cross over with ''WesternAnimation/XMenEvolution.'' Most of them are written by Red Witch. Most of the others are [[Fanfic/TheMisfitsSeries "set in the Misfit Universe"]], which means based on Red Witch's on-going series. She has several long stories, and dozens of one-shots which all spring from the premise of G.I. Joe rescuing Toad after Magneto throws him out of a plane after the end of the second season, leading to the entire Brotherhood becoming unofficial wards of G.I. Joe. Insanity ensues, though there's also been quite a bit of drama and tragedy as the series goes on.
* ''WesternAnimation/DannyPhantom'' gained some popularity in the crossover section with ''Series/{{Supernatural}}''. Since both deal with supernatural beings, it was inevitable. Similarly, it's also been crossed over with various fellow animated works featuring supernatural/magical beings, particularly ones which have depicted ghosts of some sort - there have been quite a few crossovers with ''WesternAnimation/GravityFalls'', ''WesternAnimation/AmericanDragonJakeLong'', and even ''WebAnimation/MysterySkullsAnimated''.
** A combination fandom that saw some popularity was the "Secret Trio", so named because its components - ''WesternAnimation/DannyPhantom'', ''WesternAnimation/AmericanDragonJakeLong'', and ''WesternAnimation/RandyCunninghamNinthGradeNinja'' - are all teenage boys with secret lives as supernatural superheroes battling mystical foes.
* ''WesternAnimation/ThePowerpuffGirls1998'', ''WesternAnimation/DextersLaboratory'', and ''WesternAnimation/SamuraiJack'' happen in the same world, though this might just be a mythology gag by the creators. Almost all of the shows by Cartoon Network prior to Chowder and Flapjack might qualify with ''VideoGame/FusionFall''.
* Nickelodeon plays with this, having the major shows happen across different universes that seem to intersect.
* Even before the first season wrapped up, ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' had already been crossed over a ridiculous amount of times with ''Series/DoctorWho''. Of course, considering [[MemeticMutation its already memetic status]] and the presence of background pony [[FanNickname Doctor Whoof/Whooves]], it isn't really that much of a surprise.
** More strange is the constant crossover fanart with ''VideoGame/{{Portal 2}}'', despite only sharing a very minor similarity in the role the moon plays in both series. Wheatley's promise of a pony farm down a pit probably helped too.
** Crossing ''VideoGame/TeamFortress2'' with ''Friendship Is Magic'' is very popular. Making subtle (and not-so-subtle) pony references is a popular pasttime on the official Team Fortress forums.
*** As well as lambasting the hell out of the person who made the reference.
** There also appears to be a somewhat baffling overlap with the Halo Fandom which beside Doctor Who seems to be fairly easily the most numerous crossover target in fan fics.
* ''WesternAnimation/DannyPhantom'' / ''WesternAnimation/TeenTitans2003'' crossovers are common amongst the fandom.
* G1 ''Franchise/MyLittlePony'' and G1 ''Franchise/{{Transformers}}'' are a common mash-up. This actually has a tiny piece of canon support: in the second TV special, ''WesternAnimation/MyLittlePonyEscapeFromCatrina'', the cavern where Catrina has set up shop holds several statues resembling Soundwave's minion Ravage. There was a never-animated scene for ''WesternAnimation/MyLittlePonyTheMovie1986'' where Firefly asked Optimus Prime and Shipwreck of G.I. Joe for help.
** There was also a time trying to tie G1 into ''[[WesternAnimation/MyLittlePonyFriendshipIsMagic Friendship is Magic]]'' was popular among fans that were accepting of both and liked the original mythology. The most notable is ''Fanfic/TheElementsOfHarmonyAndTheSaviorOfWorlds'', which is about the human children now adults returning to Equestria; the fic also includes other Hasbro series like ''WesternAnimation/TheTransformers'', ''WesternAnimation/GIJoeARealAmericanHero'', ''WesternAnimation/{{Jem}}'', ''WesternAnimation/{{Inhumanoids}}'', ''WesternAnimation/DungeonsAndDragons1983'' and ''WesternAnimation/{{MASK}}''.
*** Hell, ''Friendship is Magic'' and ''Transformers'' in general are common crossover fodder, and even Creator/IDWPublishing and Creator/{{Hasbro}} themselves have been known to indulge somewhat[[note]]although neither of them have made any proper crossover fiction between the two, save for Hasbro releasing a two-page promotional comic for Hascon, and even then, it also serves as a MassiveMultiplayerCrossover with other Hasbro franchises[[/note]].
* "Mystery Kids" (occasionally known as "Spook Crew") is a MassiveMultiplayerCrossover of various {{Kid Hero}}es involved in supernatural adventures. [[http://www.mysterykidsofficial.tumblr.com/ This]] {{fan film}} has the cast set as [[WesternAnimation/GravityFalls Dipper, Mabel,]] [[WesternAnimation/{{Coraline}} Coraline, Wybie,]] [[WesternAnimation/ParaNorman Norman, Neil,]] [[VideoGame/{{Psychonauts}} Raz, and Lili,]] but it's not uncommon to see {{fan art}} with [[WesternAnimation/InvaderZim Dib]] and WesternAnimation/DannyPhantom. Fan works made after 2012 might bring in [[WesternAnimation/OverTheGardenWall Wirt]] and [[WesternAnimation/StevenUniverse Steven]].
* One newer combination fandom is the "Bad End Friends", which groups together characters that each have a dark and twisted counterpart, in the show or merely in fan works. This includes, but is far from limited to, [[WesternAnimation/GravityFalls Bipper]], [[WesternAnimation/AdventureTime Farmworld Finn]], [[WesternAnimation/RickAndMorty Evil Morty]], and an AU version of [[WesternAnimation/OverTheGardenWall Wirt]] who succumbed to the will of the Beast.
* ''WesternAnimation/HazbinHotel'': Pick a character whose primary trait is killing Demons or otherwise going to Hell. Any character. Somehow, all roads for them will lead to the titular Hotel. Prominent examples include [[VideoGame/{{Doom}} Doomguy]], [[VideoGame/DevilMayCry Dante]]. [[VideoGame/{{Ultrakill}} V1]], [[VideoGame/{{Helltaker}} the Helltaker]], and even freakin' ''[[Fanfic/APeacefulAfterlife Yoshikage Kira]]''.
* ''WesternAnimation/GravityFalls'' and ''WesternAnimation/OverTheGardenWall'' have become a popular combination in general; both involve a SiblingTeam consisting of a SociallyAwkwardHero and a CloudCuckooLander, with tones that switch from silly to very creepy. It's even common enough that the CrossoverShip of Dipper/Wirt gained quite a bit of traction, and is known as [[IdiosyncraticShipNaming Pinescone]].
** While many crossovers have them meeting at their current ages (often with Mabel and Dipper winding up in the Unknown), another common trope is to have Dipper and Mabel be [[SpinOffspring the future children of]] either Wirt or Greg. (While [=GF=] is definitely in the 2010s, [=OTGW=] seems to be set sometime in the near past.) The SiblingYinYang aspect works especially well since ''Gravity Falls'' makes GenerationXerox a major theme near the end.
** To put things in perspective: Platform/ArchiveOfOurOwn lists the top 10 most popular characters in every fandom, and [=OTGW=]'s list includes Dipper, Mabel and Bill Cipher.
** Similarly, it's very common to see ''Gravity Falls'' cross over with ''WesternAnimation/RickAndMorty'' due to both shows featuring Creator/JustinRoiland, and it only became more popular with the introduction of [[AbsentMindedProfessor Stanford Pines]] and the idea that he crossed paths with [[MadScientist Rick Sanchez]] while lost in the multiverse.
* ''Franchise/CarmenSandiego'':
** There's a whole lot of {{fanart}} combining ''Literature/WheresWally'' and ''Franchise/CarmenSandiego'', what with both centering on individuals who are rather difficult to find.
** ''Film/MaryPoppins'' and ''Carmen Sandiego'' are a common crossover.
* There is a surprisingly large number of fanarts crossing ''Franchise/WinnieThePooh'' and ''ComicStrip/CalvinAndHobbes''. And with Pooh in general, as ''Pooh's Adventures'' proves.
* ''WesternAnimation/ThomasAndFriends'' and ''Tugs'' tend to cross over a lot, due to having similar subject matter (anthropomorphic vehicles), a similarly realistic setting (apart from the anthropomorphic vehicles) and the same creative team. From Series 3 of ''Thomas'' onwards, there was even an element of canon support to this, as models from ''Tugs'' were used in ''Thomas.''
* ''WesternAnimation/WinxClub'':
** It being a MagicalGirl genre has many fanfictions with ''WesternAnimation/{{WITCH}}'' and ''Franchise/SailorMoon''. ''Franchise/HarryPotter'' crossovers are also common, for the magical school theme.
** Yes, there are crossovers between ''Winx Club'' and ''WesternAnimation/MyLittlePonyFriendshipIsMagic''.
* ''WesternAnimation/GIJoeARealAmericanHero'' and ''WesternAnimation/{{Jem}}'' crossovers are commonplace because of implications that they take place in a SharedUniverse. The implications of Synergy's technology in relationship to ''GI Joe'' make for prime plot material.
* ''WesternAnimation/TotalDrama:'' At the height of the ''[[Literature/TheTwilightSaga Twilight]]'' craze, WholePlotReference fics were incredibly common. Usually Duncan and Courtney were "cast" as Edward and Bella, though it changed when Duncan/Gwen became the FanPreferredCouple.
* ''WesternAnimation/{{Amphibia}}'' and ''WesternAnimation/TheOwlHouse'' are extremely common to make crossovers between. The reason is simple: They are [[TrappedInAnotherWorld very similar shows]] created by former crew members of ''WesternAnimation/GravityFalls'' released a year apart with very FriendlyFandoms. It's to the point that it's almost {{Fanon}} that they are set in the same multiverse. Supporting this, a scene in ''The Owl House'' briefly shows Anne, the protagonist of the former show, in a news page as a missing girl, indicating the two may be actually taking place in a shared universe. Eventually, the two shows made an unofficial crossover as a script-reading at San Diego Comic Con 2021, and later a ''WesternAnimation/ChibiTinyTales'' [[https://www.youtube.com/watch?v=3faAchClwM4 short]].
[[/folder]]
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