Mega Crossover



The Fan Work equivalent of the Massive Multiplayer Crossover -- a fan-made creation combining three or more properties into a single, hopefully coherent, whole. By necessity also a variety of Alternate Universe Fic, the Mega Crossover attempts to dovetail many often wildly different settings together in the process of telling its story; it is perhaps the ultimate challenge an author can pose to himself.

When well done, a Mega Crossover can be an amazing and impressive piece of work, often epic in scale. When it isn't, it's an obvious stillborn Frankensteinian mess. Particularly bad, violently out-of-control megacrossovers, where sources are thrown together with no regard to blending their continuities, simply because the author is hopelessly in love with all those series, books, and comics, are called crossorgies.

The only problem with liking a Mega Crossover is that no matter how amazingly good it may be, trying to describe it to someone else inevitably ends up sounding corny and geeky.

Fan Fic

 * The example -- the ultimate example -- is the work known as Undocumented Features, created by Eyrie Productions Unlimited. More or less continually written since the early 1990s by a dedicated creative team, running into many many megabytes of stories, UF blends together so many sources that no one has a definitive count of them, and has successfully combined them all into a single galaxy-spanning space opera epic with an internal history of thousands of years. The earlier works are admittedly crude -- the first installment was intended as a joking "we could do something like this" example meant to be discarded when the "real" writing began -- but UF (and other EPU) stories since the middle to late 1990s have all been of exceptional quality and workmanship.
 * Also by the fine folks at EPU, Neon Exodus Evangelion starts off looking like just an ambitious Alternate Universe Fic for Neon Genesis Evangelion, but before long it becomes clear that this is a Mega Crossover world involving at least a dozen sources besides NGE, and that it only tangentially resembles Canon Evangelion. Interesting to note, that much as Evangelion was a Deconstruction, almost an assault on the tropes of Humongous Mecha, Neon Exodus Evangelion is an assault on what the authors felt was the meaningless nihilism of the original, and the fic can be somewhat hard to warm to.
 * A Game of Gods involves a group of mysterious beings kidnapping a host of beings from across the multiverse and throwing them into strange and perilous situations. The main cast of characters are diverse, and many of the worlds that the characters visit are drawn from other works of fiction.
 * Journey Through the Multiverse takes the multiverse-hopping premise from Kamen Rider Decade and Kingdom Hearts and plays it with a huge multiversal war for power, with multiple factions taking part in the war.
 * The Adventure You'd Kill For was a roleplaying forum thread game, in which fictional murderers (and a handful of legitimate soldiers) are imprisoned together by supernatural jailers and forced to work together in order to escape. Characters included the Corinthian, Sylar, the Fear, Naked Snake / Big Boss, Altair, and Beatrix Kiddo / The Bride. Belkar Bitterleaf, Dwight McCarthy, Johnny C., the Joker, Freddy Krueger, Sweeney Todd, Saruman the White, Hannibal Lecter, Bellatrix Lestrange, Geralt of Rivia, Leatherface, and many more. However a lapse in activity for several years led to it becoming an Orphaned Series.
 * Age of Heroes is a roleplaying campaign which starts with Marvel and DC which then crams in anything that can be fit in. Castlevania, Soul Calibur, Yu Yu Hakusho, and more. Now it might seem that such a campaign would collapse under its own weight, but it seems to be doing quite well.
 * AGENCY by JediAnnSolo is an adventure comic staring Shadow the Hedgehog, Sandy Cheeks, characters from Animal Crossing, DW Read, Fox, Krystal, and Marcus McCloud, Pikachu, Parappa the Rapper, and the Pink Panther. Fox, Marcus, and DW are kidnapped, causing Krystal and Mrs. Read have hired the Pink Panther (who is a Private Investigator) to find them. He has hired Sandy to help with field work, and Krystal has hired Shadow as her body guard.
 * The series has also spawned a series of non-canon pictures featuring Shadow and Sandy as a couple. JediAnnSolo has repeated said that she currently has no plans to pair them up in the actual series, but she has also said that they do make for a dynamically interesting couple.
 * And Shine Heaven Now is a humorous Hellsing fan web comic created by Erin Ptah. Some other series featured include Read or Die, Emma, Madeline, Witch Hunter Robin, Marimite, Revolutionary Girl Utena, Scooby Doo, a hentai doujinshi Kouta Hirano did before Hellsing, Jeeves and Wooster, and Little Orphan Annie.
 * In a nutshell, Shine crosses Hellsing over with everything you'd expect and quite a number of things you wouldn't.
 * The Ultimate Crossover Movie is the series that crossovers everything from anime, cartoons, video games, and films to real life. It's mainly conspiracy theories and related stuff. Early versions can be found here and here.
 * Arisugawa's Locket has a cast of "regulars" that includes characters from Revolutionary Girl Utena, Sailor Moon, Tenchi Muyo!, Excel Saga, Hand Maid May, Vision of Escaflowne, and Ranma One Half, and that list gets longer as the story goes on. The "guest stars" can come from, well, pretty much anywhere in the anime world, and on rare occasions, a live action show like Buffy the Vampire Slayer. The rampant crossing over is explained by the fact that Washu equipped the titular bar with a version of her Time and Space device, allowing it to exist over multiple dimensions.
 * The Battle Fantasia Project, where the nationally televised attempted suicide of a magical girl reveals the existence of magic to the world, and the existence of magical girls to eachother. Includes Sailor Moon, Lyrical Nanoha (post-A's), Cardcaptor Sakura, Kämpfer, Puella Magi Madoka Magica all the Precures and others.
 * Both Syllables combines Invader Zim, Liloand Stitch, and Buzz Lightyear of Star Command.
 * While Chess Piece is primarily a Danny Phantom based webcomic, it has enough characters from other Nicktoons intertwined in its story to constitute its own kind of Mega Crossover.
 * The massive Chicago Convergence includes characters from Another Fine Myth, Bolo, Buffy the Vampire Slayer, Charmed, Catch-22, Dark Angel, Diagnosis: Murder, Doctor Who, Due South, Early Edition, Forever Knight, Friday the 13th: The Series, Hammers Slammers, Highlander, Indiana Jones, Knight Rider, Kung Fu The Legend Continues, The Lord of the Rings, Love and Curses, MacGyver, Martial Law, Mechwarrior, Men in Black, Murder, She Wrote, Nash Bridges, Kolchak the Night Stalker, Quantum Leap, Quincy, Relic Hunter, Seven Days, Sliders, Space: Above and Beyond, Special Unit 2, Stargate SG-1, Star Wars, The Terminator, The Black Company, The Incredible Hulk, The Pretender, The Sentinel, The Wizard of Oz, Time Bandits, The Time Tunnel, The Transformers, Viper, Walker, Texas Ranger, and The X-Files all coming to Chicago. It manages to stay both coherent and hilarious.
 * Convergence is another one, set on Babylon 5, from the late 90s. Politics and squabbling between the many authors eventually drove everyone away.
 * Usually, a Mega Crossover will contain either anime or Western Animation, but not both. One of the few exceptions is CrossWorld: Episode 1, by Hejin57, a.k.a. Kareem Elamrani. This is an unfinished work containing, so far, characters from Dexter's Laboratory, Codename: Kids Next Door, Sonic the Hedgehog, The Nightmare Before Christmas, The Powerpuff Girls, Samurai Jack, and, of all things, Suzumiya Haruhi. It's about as cracky of an idea as one would expect, but actually isn't that terrible, despite the fact that it's not nearly as good as the other fanfics by the same author. Unfortunately, it hasn't been updated in over a year, which actually wouldn't be so bad if the author hadn't stopped just when the story was starting to get good. The author has since chosen to work on his other, non-crossover Haruhi fanfics, which as has already been mentioned, are much better works.
 * The same author has also written Cross Chronicles, a more conventional Mega Crossover of Suzumiya Haruhi, Kenichi: The Mightiest Disciple, Tengen Toppa Gurren Lagann, Midori no Hibi, and Fate/stay night. What's more, the fanfic itself is set in the universe of Valkyria Chronicles. Interestingly enough, even though the two fics are completely different, the same Plot Device is used to get all the different fandoms together in both of Hejin's Mega Crossovers.
 * John Biles' Dance of Shiva blends five classic Anime -- along with cameos from and Shout Outs to at least a dozen other sources -- to create a story that is by turns action-packed, comedic, and unabashedly mystical.
 * Danny Phantom Rebirth is yet another Danny Phantom Mega Crossover webcomic.
 * DDM: Digimon and Duel Monsters blends elements and characters from Digimon, Yu-Gi-Oh!, Cardcaptor Sakura, and Pokémon into a single setting.
 * ''Doctor Who: The Manga Starts with the Eleventh Doctor asking Trisha Elric to take in a little girl who is on the Run from Providence who are working on recreating The Technology of the Tititular characters of Livewires to create an Army of keyblade weilders, and that's just the first three pages...
 * Drawing the Line stars just about every animated character Stephen Colbert has ever played. Let's see -- Stephen hires Stephen to sue Jon, who hires Stephen to defend him...
 * The Emiya Clan is a forum community-created series of omakes/snippets based from Gabriel Blessing's In Flight, featuring a theoretical GOOD END to the story that involves the next generation of children resulting from the inevitable harem. There's easily over a dozen regular "authors" and even more regular forum goers who swap ideas and characterization analysis with each other. It involves Loads and Loads of Characters, most of them OCs on which of course, YMMV.
 * The forum itself has actually imposed upon itself a strict code of discipline and mutual convergence to root out any wanderings into Mary Sue territory, Fan Wank, or other forms of Sturgeon's Tropes. Because of the nature of the community, new authors are added regularly, but work quality and content is kept in line by a democratic system for new crossovers and ideas that will be accepted as {Canon}.
 * Currently the Clan features Shirou Emiya, 24 wives, and 28 children (Further additions have been capped at this number). This is not counting various relatives, family friends, and clientele that show up in the stories on a regular basis. Usually, each child gets their own crossover(s), while the entire family (or a part of it) may participate in a story sometimes.
 * A few of the authors have compiled their works here (many more stories have been added past this point).
 * Eureka, A fanfic that contains Ranma 1/2 and Eureka at its core, works the idea that there's another division of "Eureka". Namely, there's the American Normal Science Branch, and the Japanese MAD Science Branch. In the end, it includes Ranma 1/2, Eureka, The Road To Cydonia, Dragon Ball Z, Chobits, Project A-ko, Tenchi, Neon Genesis Evangelion, Cooking Master Boy, Yu Yu Hakusho, Bleach, Kim Possible, Venture Brothers, Knight Sabers, Robotech, Naruto (Naruto is actually only acknowledged as a manga, but still helps the cast), All Purpose Cultural Catgirl Nuku Nuku, Pokemon, Dexter?s Lab, Jimmy Newtron, Invader Zim, X-Com, Men in Black, Pinky and the Brain, Full Metal Panic, Power Puff Girls, My Life As A Teenage Robot, Marvel Comics, Stargate SG-1, Power Rangers, Sailor Moon, Dark Titans (a fanfic), Raiders of the Lost Ark, and Gundam as, usually, vague little references that you will miss unless you know that series/movie/setting. However, some of them also play larger roles, or more obvious appearances. Anyone who wants to spend the time linking to those respective series feel free to do so, because I'm not
 * Errors in Continuity.
 * The Fandom Wars is a standard example of a Mega Crossover, though it concentrates almost entirely on the two factions of the My Little Pony: Friendship Is Magic World, whom are being internally manipulated into participating in the War that they didn't want to join in the first place, and the Anime Faction, one of the 'Big Three' major military powers and most likely (at least at first) to win. The series can be found in four parts. Be warned that it is very middle-tier.
 * Fictionalization IV, a Game Mod for Civilization IV, does this for pretty much all of fiction.
 * Dracula's armies of toy soldiers Vs. Dr. Doom's flying saucer? HELL YEAH!
 * Glad you like it! (I'm the creator. No really.)
 * The Finale of the Ultimate Meta Mega Crossover. Featuring A Fire Upon the Deep x The Melancholy of Haruhi Suzumiya x Ah! My Goddess x The Incomplete Enchanter x Book of Amber x Callahans Crosstime Saloon x Buffy the Vampire Slayer x Star Wars x Robert Heinlein x Shinji and Warhammer 40 K x Thousand Shinji x Once More With Feeling x RE-TAKE Of Evangelion x Discworld x South Park x The Matrix. In the first 1400 words.
 * Oh, and it also has Mr. Rogers from The Ultimate Showdown Of Ultimate Destiny.
 * This reaches almost Lovecraftian proportions when it goes on to include Of course, most of them are off-screen.
 * Grand Tour Started as a Ranma One Half and Star Trek (both Star Trek Deep Space Nine and Star Trek Voyager) crossover, it quickly spiraled into more series, including Lyrical Nanoha with many series acting as a one-chapter one-shot or a cameo mentioning at most.
 * The last chapter tops practically everything when it comes to fight scenes.
 * And now it's complete. What a ride.
 * Update! Now with a sequel! Awesome.
 * Hybrid Theory by Blade and Epsilon viciously satirizes the Mega Crossover by presenting such a world -- but then having some of its inhabitants realize that it couldn't possibly have existed before a certain point because of the conflicting backstories of its component parts.
 * The Insane Quest, a Play By Post Game, is an odd example. While it does take place in a universe that crosses over with Super Mario Bros., The Legend of Zelda, Pirates of the Caribbean, Naruto, Pokémon, One Piece, No More Heroes, and Pandora Hearts (among others), none of the characters from these series are the main characters. Instead, the story focuses on a cast of original characters and settings created (mostly) from scratch by the Game Master and the participants of the game, with the characters from the above series only appearing as supporting roles, cameos, and occasionally antagonists. But other than that, the concept is pretty much the same.
 * The fic Kingdom Crossovers fuses a lot of things, with Zim being the keybearer and going from everything, from Garfield to Warhammer 40000. Needs a Better Description.
 * Due to the Massive Multiplayer Crossover nature of Kingdom Hearts, many fanfics based on that canon will also use it as a catch-all explanation for blending together pretty much anything and everything. Just explain it as a new planet and there you go.
 * Tsubasa Reservoir Chronicle is subject to this too for the same reason. There was actually a very short-lived (thank the heavens for it) fic with Tsubasa and Kingdom Hearts crossing over.
 * The Life After Death Trilogy by SilverGryphon8 and GamineMadcap is, to start with, a Spider-Man 2/A Midsummer Night's Dream crossover starring Doctor Octopus and Robin Goodfellow. It is confirmed by the authors that the list of crossovers and cameos will include: Daredevil and most of the Marvel Universe,Bones, the Cal Leandros books, The Dresden Files, The Sorcerer's Apprentice, Doctor Who, and more.
 * Dreamwidth is host to an ever-increasing number of what are called multifandom roleplaying games. Some rewrite characters to fit new settings, but most are true Mega Crossovers, bringing characters together from their home canons. Drama Drama Duck, for instance, uses the premise that people from different universes are somehow able to communicate with each other over the Internet (including people who can travel between worlds, allowing characters to meet face to face). Individual games can have very different setups, genres, possible restrictions on acceptable characters or canons, and guidelines like the involvement of OCs or canon OCs.
 * Lynching ITP is a cross between this, an Eragon / Twilight Hate Fic, and a set of Play-By-Post Games.
 * Marios Day Job: A webcomic starring Mario and Luigi of Super Mario Bros. fame as (apparently) the only plumbers in Video Game Land. Linked universes include The Legend of Zelda (mostly Ocarina of Time flavored), Pokémon, Harvest Moon (which could count for this trope on it's own) and Animal Crossing.
 * The Massive Multi Fandom RPG, Tvtrope's own Mega Crossover Play By Post Game. The premise: a mysterious, all-powerful being known only as The Troper has ripped dozens of characters out of their universes and dumped them into an enclosed city with no way out. Each new day the city's inhabitants are subjected to a new, often absurd, scenario called a "curse" -- having their genders reversed, being transformed into animals or being transported into a dinosaur-infested jungle. The game has included characters from Pokémon, Fullmetal Alchemist, Ghost Recon, Valkyria Chronicles, X-Men, Mass Effect, Lost, Star Trek, Danny Phantom, Halo, Tengen Toppa Gurren Lagann, Metal Gear Solid, No More Heroes, Star Wars, and Kingdom Hearts among many, many, many others.
 * Season 2 began almost as soon as Season 1 ended, and has already featured characters from Soul Eater, Mega Man X, Firefly, Lyrical Nanoha, Yotsuba&!, Green Lantern, Neon Genesis Evangelion, Castlevania and more.
 * Maverick9871 has a habit of starting with a decent story idea, but within a few chapters the story spend more time introducing new crossover material than on the original idea.
 * MegaMan Battle Network: A NetNavi and a Mew Mew Is novelization of the seven Battle Network games with a crossover twist.
 * Mirrors Multiplied is one of the earlier and more well-known Ranma 1/2 Megacrossovers on the net.
 * My Life as a Teenaged von Neumann Device primarily focuses on My Life as a Teenage Robot, but is absolutely loaded with subtle and not-so-sbutle references to other Nickelodeon and Cartoon Network cartoons. Among other things, the Cluster has been having trouble with the Irkens and the Yugopotamians, and Dr. Wakeman's old college roommate was Dr. Ghastly.
 * Rob Morris' "The Never-Ending Battle". Take M*A*S*H as the core fandom. Add in that several of the characters just happen to be Highlander-style Immortals and that before becoming Mulder's nemesis the Cancer Man was running experiments in Korea in the early 50's. Oh, and Sherman Potter is descended from a BtVS-style Slayer and came home from WWI with one Nick Knight in tow. Then there's Hawkeye and Hot Lips' roles in the Eugenic Wars from Star Trek, not to mention the way that most of the human crew-members of Deep Space Nine can trace their family bloodlines back to someone who served at the 4077th. And let's not forget about BJ's wife Peggy... and her half-sister Samantha Stevens. By the time Godzilla shows up you don't even bat an eye. Of course Godzilla and M*A*S*H can co-exist in the same universe -- giant lizard monsters aren't really that strange.
 * Neverending Struggle: Multiverse at War is a forum RPG based entirely on this trope. Basically, in a world where all fictional characters live, a war breaks out. Each separate faction (Individual Armies) is trying to take over the world. It has an incredible amount of 3 players, probably because of lack of advertisement.
 * Also, from the same person who manages that, comes Ookami no Monogatari and Wolfeye City. Ookami no Monogatari is about a group of characters from different dimensions (fictional works) ,at the moment, One Piece and Megaman X, being lead by a teenage girl to various missions. Wolfeye City also uses the Author Avatar trope, since it's about Alter-Egos, the comic representations of the author and some of her friends, fighting demons who are trying to destroy the city, who is filled with anime and video game characters. All three are Better than it Sounds. Though, Erase Alpha, the author, must love this trope.
 * All three are dead. And now Neverending Struggle V2 and IMAGINE, both Mega Crossover RPGS (not very active at the moment though).
 * Never Too Young by Koolkame. Ben 10, WITCH, Danny Phantom, The Life and Times of Juniper Lee, American Dragon Jake Long, with cameos from Mahou Sensei Negima, Back to The Future The Animated Series, X-Men: Evolution, Justice League Unlimited, Fantastic Four and Jonny Quest. Expect Loads and Loads of Characters.
 * Nicktoons Tales is a fancomic that sews all Nicktoons settings into one planet, as well as original characters living on that planet.
 * Also, in the same series, there is a planet with all anime settings sown into it.
 * Nuclear Fusion on the Anime Adventure. Noteworthy because it manages to mix up elements of over one hundred completely unrelated series and manages to combine them into a single massive Fallout inspired Post-Nuclear world, and not only make sense, but tell an interesting and unique story.
 * Obscurité Musicale is an active RPG that crosses over, mostly,Phantom of the Opera, Sweeney Todd, and Les Misérables-- as well as Jekyll and Hyde, Billy Budd, and Spring Awakening. As well as one or two actual historical figures, and a less-vampiric Herbert von Krolock. You guessed it-- it's very, very AU, but serious in tone. The in-character chatbox can't have the same said for it, being the ungodly place that spawned the pairing of Edward and the Corinthian. They're both on crack, of course. Just different kinds of crack. It's... weird. Some parts hang together fairly well. Some are a bit weird.
 * Are you calling my board weird? Note that neither the Corinthian nor Edward Cullen are viable canons for this board. Note also that it's set in a very not-accurate quasi-English France. Nitpickers beware. I mean, they are musicals... And expect Oliver! canons shortly. We're that expansive. Unless you want to try and Steampunk it up. Then the answer is no.
 * That's good weird. I play on it, and love the place more than probably any other site on the internet.
 * The Open Door by Academia Nut. The core premise carries Neon Genesis Evangelion/Warhammer 40000 from the previous work, Thousand Shinji, that of the Chaos gods expanding and finding ways to defeat the C'tan, with the first chapter involving The Melancholy of Haruhi Suzumiya. The third chapter hits Stargate SG 1, the sixth hits Star Trek the Next Generation, the twelfth hits both Buffy the Vampire Slayer and Lyrical Nanoha simultaneously, and steadily more universes are involved. There is something of a consistent multiverse system laid out, but the specifics are difficult to summarise.
 * Overkill starts out as a Naruto/Nanoha crossover, and then becomes the author asking, "How many fictional characters can I conceivably put in this?"
 * Phoenix Wright Anime Attorney is an AMV that's edited in a way that makes it seem as though Phoenix Wright is interacting with characters from various other anime series.
 * Ellen Brand's Personality Conflicts universe melds Power Rangers with a spade of unrelated properties, including Danny Phantom and Detective Conan, but her masterpiece is probably the Trial Arc, where the Rangers are forced to defend Zordon in galactic court for his actions over the course of the series, while a resurrected villain forces the VR Troopers, Beetleborgs, Masked Rider, and previous crossover allies the Ghostbusters to defend Earth. Also notable as the storyline provides a "proper" finale for each of PR's sister shows.
 * PRIMARCHS not only pulls this off, but justifies it from the 2nd arc onwards by the inclusion of an entity called the Plot Hole.
 * Process of Elimination starts off primarily as a Ranma 1/2 and Tenchi Muyo! story, but has many additional anime added to its story.
 * Prodigy, Holy crap. This story is actually pretty damn insane, and not just for the fact that it's a crossover between, ahem: Harry Potter, Crime Scene Investigation, House MD, Grey'sAnatomy, Numb3rs, Psych, Law and Order:Special Victims Unit, Naval Criminal Investigative Services, and possibly even more. No, I'm not kidding. Nearly the entire damn story (Which is 140,841 words, if I may add.) is so damn awesome. Words don't describe it, while it does have the thin base of a lot of HP AU's (Harry Potter's twin is named BWL, Harry is ignored.) If runs away with it and crashes that idea into a building, then lights the building of fire. This is easily in the Crowning Moments Of Funny as well.
 * Similarly, Prophecies? We Don' Need No Stinkin' Prophecies by Greywizard (also on Twisting The Hellmouth) shows a Buffyverse where Harry Potter was raised by a married Xander and Buffy, and the forces of the Watcher's Council include characters from, according to the author: Tears of the Sun; Blackhawk Down; White Sands; ER; Witchblade; Supernatural; Raven; PSI Factor; City of Angels; Under Siege; Chicago Hope; Stargate SG-1; The X-Files; NYPD Blue; The Craft; Rogue Warrior; the Tom Clancy novels; X-Men; Rainbow Six; Law and Order; the Lethal Weapon movies; the Amber books; Alienversus Predator; Practical Magic; Phoenix Force; and Sabrina the Teenage Witch. (Plus another Buffy fanfic, plus Buffy and Harry Potter themselves, for a total of 29 sources.)
 * Roommates (2007) and its Spin-Off s Girls Next Door and Down the Street are fancomics on Deviant ART, that bring various fictional characters together in an out of canon world. The main characters are from Labyrinth, Les Misérables, Phantom of the Opera and Pirates of the Caribbean (DTS adds Dracula and Frankenstein) with countless cameos Shout-Out s etc..
 * The Secret Life of Dolls, A Dollfic by Cleolinda Jones, writer of Movies in Fifteen Minutes.
 * The Disney/NonDisney editor community on YouTube does this often in their videos but seem to be having their own crossover event with a project called The Sixth Sense. It involves an amalgam of plots reminiscent of X-men, witch hunts, government conspiracies, giving various animated characters powers and having them interact. Already, people have mini-storylines and connections to other characters which will probably continue into the official project.
 * It has also inspired a fanfiction which can be read here.
 * Sleeping With the Girls, by Admiral Tigerclaw, is essentially a Deconstruction of the Self Insert fic, in which a normal guy (albeit one who's been through boot camp) is thrust into various fictional worlds by an unusual mechanism: He 'jumps' to each world the moment he falls asleep, and he wakes up in the same bed as a female character. Naturally, Hilarity Ensues. Note that the action scenes are military-focused (with good reason) and many times more epic than you may remember them being in that particular episode.
 * SNAFU comics have several webcomics that are crossovers. The most crossover-ish of them are Powerpuff Girls Doujinshi and Grim Tales from Down Below, which feature crossovers of almost every Cartoon Network and Nickelodeon cartoon (mostly, indeed, from CN).
 * Sonic the Hedgehog: Rise of Nazo is a Mega Crossover that is based on Nazo Unleashed. Two more Mega Crossovers followed after it.
 * Another Sonic Mega Crossover Catch Me if you Can has Dr. Eggman skillfuling dupeing a pack of Magical Girls to attack Sonic. This is one of his most clever plots as Sonic is shown to have gynophobia.
 * And then there's another Mega Crossover called Multi-Dimensional Melee! which manages to include some pretty unlikely characters, and yet primarily focus on Sonic. The story follows an accidentally familiar plot which includes a Crack Pairing, several Original Characters, Fourth Wall breaking, a faceless plot orchestrator, and a seemingly decent amount of followers. Several continuity nods and series trademarks are also thrown here and there.
 * Suburban Senshi, which brings in all sorts of series into the Sailor Moon universe.
 * Justified (well, as justified as such a thing can be in the fanfic industry) in the Sailor Moon Expanded universe; a method of trans-dimensional travel allows characters from the Sailor Moon universe to travel to other dimensions on the conceit that every anime and manga ever produced has its own separate universe. The various Dark Kingdom Renegades seemed to run into this quite often in their early years on Earth, having traveled to the worlds for Bubblegum Crisis and Ranma 1/2 just for starters, and later to Urotsukidouji (aka Legend of the Overfiend), where Titanite (youma Sailor wannabe, for those just joining us) encountered said Overfiend. With her disguise device set to Sailor uniform... and broken. Thankfully, the author managed to avoid following the obvious to its conclusion in a manner most awesome. And in an unfinished story, Titanite finds herself in Neon Genesis Evangelion, and unfamiliar with the series, tries to understand it in terms of the classic Humongous Mecha shows she's seen in the past.
 * To make things doubly interesting, the laws of these various dimensions seem to apply themselves to trans-dimensional visitors over time. Thus, in the Ranmaverse, Calcite takes on the mannerisms of a wizened martial arts master, and felinoid Margrave becomes even more catgirlish than usual. The DKR use this to their advantage; as long as they remain in the Sailor Moon universe and work on behalf of the forces of good, they are nigh indestructible.
 * Spongebob 2019 brings almost all of the Nickelodeon characters together to defeat a now out-of-character and power hungry Spongebob Squarepants, with appearances from other shows that aren't originally from the main Nick lineup like Beavis and Butthead (MTV), Blue's Clues (Nick Jr.), Degrassi, H₂O: Just Add Water (Teen Nick) and Power Rangers Samurai (This airs on Nick in the US, but not really a Nick original).
 * Super Milestone Wars
 * Super Milestone Wars 2
 * Kamen Rider x Super Sentai x Super Milestone Wars: Crossover Taisen is a crossover of Super Milestone Wars 2, Kamen Rider and Super Sentai.
 * Survivability tells its own plot in the Bleach universe through K Pop characters (from at least 4 different fandoms).
 * Sweet Dreams has Labyrinth, A Nightmare on Elm Street, Inception and The Sandman.
 * Takamachi Nanoha of 2814 fuses together Lyrical Nanoha, the DCAU, Fate/kaleid liner Prisma Illya, Mahou Sensei Negima, Sailor Moon, and Cardcaptor Sakura in a hilariously awesome story. It begins with, shortly before becoming a Magical Girl... Nanoha ends up becoming a Green Lantern. The story obstinately is going through the first two seasons of Nanoha, with more and more craziness added in thanks to the crossovers.
 * Anything by Shadow Crystal Mage will invariably become this once it has enough chapters. Special mention also goes to Raikiri Triken.
 * Tales From The Barman... and Tales From The Barman... Part II implement a megacrossover through the device of a bar run by Xander of Buffy the Vampire Slayer, in Cleveland after the end of the series. Each chapter is its own small crossover fic, ranging from vignettes to full stories, with characters from dozens of settings ranging from Michael Moorcock's Eternal Champion to Cheers making an appearance and telling their tales.
 * Tales Of Toons: Knight of Lolicon, which was shilled on this wiki, and is a crossover of Dragon Ball GT, Transformers, Inuyasha, One Piece, Naruto, Sailor Moon, Cardcaptor Sakura, Demashita! Powerpuff Girls Z, Futari wa Pretty Cure, Mermaid Melody Pichi Pichi Pitch, Ah! My Goddess, Love Hina, Petite Princess Yucie, Suzumiya Haruhi, Negima, Pokémon, Digimon Tamers, Yu-Gi-Oh!, Zatch Bell, Rozen Maiden, The Legend of Zelda, Star Ocean, Xenogears, the Tales (series), Final Fantasy, and  It's... out there.
 * Author Tenhawk is almost as notorious for this as he is for writing nothing but Xander-Sue.
 * The story The Terran Jedi over on Twisting The Hellmouth throws in many random cameos into a story where Xander is a Jedi Master, including but not limited to Stargate, Discworld, Torchwood, Harry Potter, and Frasier (of all things).
 * The Stargate parts have become so frequent and so large that they have long since gone beyond cameos, and at this point it reads like a straight crossover.
 * The Three Kingdoms is another mega-crossover involving characters and objects from different game franchises, novels, movies and anime to suddenly start appearing in our world at December 21 2012, marking the Doomsday. After a short amount of joy, politics decided that these 'newcomers' were dangerous due to their magic capabilities, superior technology and other abilities. An event called Bad Apple Event led to Hakurei Reimu from the Touhou video game franchise annexing the entire US which could be read on the prolouge. The Vocaloids and Miku eventually caught wind of the event and decided to annex other countries in the name of protecting them from Reimu. Of course, eventually, the kingdom of Gensokyo and Yamaha formed with war between them. They were soon joined by Haruhi no Suzumiya after realizing her god-like powers. By then, the three kingdoms have formed and the crossover 'The Three Kingdoms' led to Haruhi planning an invasion. This mega-crossover contains a variety of different creations. (From HMS Thunderchild, Alex Mercer, Familiar of Zero, Star Wars, Strike Witches, Metal Gear and even One Piece)
 * Three Messengers is somewhere between this trope and a Crossorgy. Production at present is slow because of how much there is that the author isn't sure about in one of the source works.
 * TKR2, a now-defunct massive fanfic series by multiple authors started off as a fairly straight Knight Rider/Team Knight Rider fanfic, then expanded to cross over with Star Wars (a lead character becomes a Jedi Master), then Star Trek (another lead character becomes a Borg queen. One episode has our heroes on a chase across dimensions, culminating in the Starship Voyager landing to help talking cars fight Darth Vader, while a young Gene Roddenberry, Glen Larson, and George Lucas, who had apparently been out necking, look on), The Invisible Man (He gets a talking car), Highlander (yet another character is an immortal. And also a Jedi), Hercules: The Legendary Journeys (In a very complex crossover, a character described as looking like Kevin Sorbo teams up with the real Kevin Sorbo, and also Hercules), Teletubbies (They're evil aliens), Barney (He's A Great Old One), James Bond (He teams up with our heroes to stop a supervillain plotting to build a giant lightsaber with which to cut the earth in half), and Survivor. Really.
 * Chris Davies' Together Again crosses over several anime, including Gall Force, Sailor Moon, Neon Genesis Evangelion, and many more, along with numerous non-anime sources including Star Wars, GURPS International Super Teams and DC's Sandman.
 * Top Dog, by Doghead Thirteen, is a shared universe with several different storylines happening at once; the three main stories involve very AU versions of Harry Potter, Ranma ½, and Naruto. It pulls in characters and references from everywhere under the sun, including Tenchi Muyo!, Firefly, Star Wars, Star Trek, Girl Genius, Sluggy Freelance, and more. This list is very incomplete; the author is a fan of Undocumented Features and says that Top Dog is approaching its level of crossoverness.
 * The Traitor Game is like CLUE. Except with various fictional characters dropped into a setting and violently murdering people amidst a usually epic background. So far, we've had Trigon getting beat up by Asuka, Rei, Cyborg Superman, Doctor Doom 2099, and a slew of others by the usage of Yellow Lantern rings... actually, just go read the summaries there.
 * The Travelsverse is a collection of both Nintendo and other game series that are connected via Super Smash Brothers, by Bulbagarden Member Instrutilus. Though a majority of the action seem takes place on Sinumonas, the name of the Pokémon World here, the person in charge, Instrutilus, has expressed interest in looking at other series to help connect the universe, rather then just having Link and Samus live on the planet and several references to the Super Smash Brothers Core, a collection of the universes greatest fighters that was named after an old tournament they once participated in.
 * TRES is a lesser known webcomic which stars several characters from different anime and has a Tsubasa Reservoir Chronicle influence.
 * Ultimate Crossover Wrestling combines not just wrestling organizations (WWE, TNA, etc), but anime, games, tv and movies.
 * Unity is for the most part simply a crossover between Star Wars and Star Trek, albeit an exceptionally large and epic one. Then suddenly its last few chapters involve Seven of Nine and Mara Jade crossing into all kinds of other franchises: Halo, Hellraiser, Wing Commander (where they note the resemblance a character played by Mark Hamill has to Luke), Night of the Living Dead, War of the Worlds, the Marvel Universe, Transformers, The Lord of the Rings, The Hitchhiker's Guide to the Galaxy, Alien, and Battlestar Galactica. After that last one, Number Six even tags along and plays a key role in the final battle.
 * Vathara's Urban Legends universe, which includes or alludes to easily twenty or more series.
 * Chris Jones' short story The Virus -- which was a originally a simple crossover between Ranma 1/2 and Tenchi Muyo! with a few cameos from other series -- expanded unexpectedly into a shared-world megacrossover where characters from dozens of fandoms had to deal with the after effects of a Juraian virus which had incorporated Ranma's gender-bending curse into itself, and then transmitted it permanently to every living human.
 * Years ago there was a combination fanfic/webcomic called The Wrath of Invincar. The main characters of Slayers and Vision of Escaflowne, who had been placed in a Gilligan's Island-esque setting, set out on a quest to defeat...a green Smurf, with hilarity ensuing along the way. Such antics included Gaav settling an argument with Phibrizzo by pinning him beneath the Mystery Machine; much mockery by the French knights; and a showdown between Lina Inverse and Quick Draw McGraw. Sadly, the story has since been taken off the Internet for space reasons.
 * There's this?
 * The story was based in the same universe as those fics, but it was done by another author (all that's left of it now is the introductory page). Thanks for pointing those out, though.
 * Yukari Is Free is a crazy, hilarious Mega Crossover that takes place primarily in the Azumanga Daioh universe. It is interactively written by several authors on a daily basis. Parodied elements of virtually everything, including Yotsubato, Tsukihime, Tengen Toppa Gurren Lagann, Code Geass, Real Life, Portal, WALL-E, Star Wars, and Team Fortress 2, just to name a few, have each made at least one appearance.
 * Yu Yu Gi Digi Moon is an ambitious crossover between Yu Yu Hakusho, Yu-Gi-Oh!, Digimon Tamers, Digimon Frontier, and Sailor Moon. Later stories include Digimon Adventure, Digimon Adventure 02, Yu-Gi-Oh! GX, and Yu-Gi-Oh! 5D's.
 * Where on Earth, Spies is a Web Serial Novel that began as a crossover between Where's Waldo and Carmen Sandiego in which they are the best agents at two competing secret agencies. Foe Yay Ensues. After the first chapters, the author expanded into other properties, incorporating (among others) the GEICO Gecko, Erin eSurance, and Allstate's Mayhem. It can be found here.
 * ''Megas: Final Wars, a fanfic that combines Megas XLR with Phineas and Ferb, Harry Potter, Lilo and Stitch, Super Sentai, Kamen Rider, Metal Heroes, and Commander Keen. It also serves as a Grand Finale for Megas XLR.
 * Dave Stdider Pokémon Traner takes every character from everything you've ever loved, strips them of their canon personalities, and throws them into the pokemon world without explanation.
 * Nobody Dies. Just off the bat, there's Neon Genesis Evangelion, Portal, Mass Effect and a healthy dose of Transformers, to say nothing of the three different Evangelion continuities that the author decided to throw into the pot.

Fan Vid

 * The grandaddy of all Fanvids is the Daicon IV Opening, made for a Japanese anime convention in 1983 by a group who would go on to become Studio Gainax. It's impossible to list (although somebody tried) all the sci-fi, fantasy, movie, comic book and game references found in these five incredibly animated minutes.
 * Dead Fantasy unites (mostly) female characters from Final Fantasy, Kingdom Hearts, and Ninja Gaiden as they end up having to fight each other in very brutal ways.
 * Niconico video list Muv-Luv Crossovers, blends the Unlimited storyline of Muv-Luv, and spliced it with Gunparade March universe, in addition to having characters from Zegapain. Running parallel to the story is the Planet Fairy setting of Sentou Yousei Yukikaze, in which Ryu Sohma becomes the copilot to Rei Fukai after his transformation from Takuto Kaneshiro. And both worlds are fighting what seemed to be a combination of JAM, BETA, and/or Festum, and it seems that . The story is told in Visual Novel-style dialogues interspersed with footages from anime/games related to the media, as well as careful splicing to ensure that everything is consistent. The "opening" animation of the series proper is in the second episode, but while it starts with Muv-Luv setting and the beginning of Argento Soma, Yukikaze's arc proper starts at episode 6. As of 12 February 2011, the series has 10 episodes ranging from 20 to 30 minutes. Unfortunately, since the series is very heavy on dialogues, non-Japanese speaking viewers would have quite a problem in following it.
 * Many MUGEN video series on Youtube, when they're not just series of fights, will be a Mega Crossover, such as:
 * The 7th Moon MUGEN series by angeldagdag
 * The HvH MUGEN series by solkenneth003
 * DRB Origins, ODC Wisdom and ECE Mystery by TheOfficialFallen

Fan Game

 * Gokou Sama(aka Somarinoa or Thor Steinbach) is currently working on following Mega Crossover Video Games: Ultimate Showdown(top down action game about characters from everything engages massive duel of death) and Amalgam Online(Alien-themed Mega Crossover Strategy game)
 * Mushroom Kingdom Fusion, a fangame-in-progress, sends Mario and Luigi (later a host of others) across a few of the most famous gaming franchises in order to bring down Legion before he can successfully fuse all worlds and drain the energy from the reaction...or something. The creators are keeping the plot a secret -- will they finish before it becomes the gaming equivalent of a Dead Fic? Given the ambition of the project, I'd have to guess no...but hey, we know Solid Snake is mentoring them! If that doesn't make it awesome, what does?
 * And it's sister project 'Super Mario Fusion Revival'. Which, though more Mario-centric, still features levels and areas from many other franchise once outside the first world. A smaller and less ambitious project then MKF, but built with a stronger engine and with great care put into each stage. Take a look for yourselves.
 * Card Sagas Wars (see here) is another ambitious fangame, combining many characters from several different games. It's the sort of thing that can only exist due to dedicated fans or else the legalities of it would make everyone's heads spin.
 * Xeno Fighters R, a Bullet Hell Shmup featuring ships and characters from Gradius, Raiden, Legendary Wings, Twinbee, Galaga, and even Pokemon.
 * MariO takes the original Super Mario Bros. and gives Mario a Portal gun.

Other

 * Heroes and Monsters of the Milennium Is a conversion for the Unisystem RPG ruleset, mixing Buffy the Vampire Slayer/Angel with everything from Marvel and DC Comics to Stargate SG 1, Godzilla, Ultraman, Lyrical Nanoha, Gargoyles, Negima, the works of H.P. Lovecraft, Mazinger Z and many others. With considerable overlap in themes, races, and technology.
 * Ani-Mayhem, a Collectible Card Game produced in the middle 1990s by Pioneer Entertainment that set characters from many different anime settings -- surprisingly including many series licensed by companies other than Pioneer -- in a grand romp across their various worlds.
 * So Who Wins, a any character battle website which a crossover between anything can happen.

Real Life

 * World War Two has something for everyone. Those Wacky Nazis? Check. Dirty Communists? Double-check. The British fighting on The Home Front? Yup. Eagle Land pulling a Big Damn Heroes moment for Europe (only after the aforementioned communists had already lost 20 million people)? Why not? And let's not forget about the Nuclear Option being used in the East. Everyone got involved in the second World War -- especially states that claimed non-involvement such as Spain or Switzerland.