A Cross Over that involves characters from more than two shows or more than two fictons.
More often than not, this is a mash up of series which do not have a strict sense of continuity or a clear Universe Bible. To lessen canon-faulting, especially with series that do have strict continuity, a new 'neutral' setting is made that offers equal footing for all the characters.
This rarely occurs in live action shows, unless a production company can be formed that holds copyrights to everything. Thus, this is much more common in animated series — although you can generally expect The BBC to pull one out of somewhere when Children In Need or Comic Relief rolls around.
It also becomes more viable the farther you get from canon, such as one-time TV specials and especially video games (Kingdom Hearts, Jump Super Stars, Super Robot Wars, etc.)
As Story Arcs have become more prevalent, this practice has somewhat lessened, with shifts to strict Verse building and explicit references.
This trope has become increasingly common in video games, especially those involving both licensed and original properties. These games, depending on how far or how deep they mine, can have interesting effects on the fiction chosen. Many long-gone and/or forgotten Humongous Mecha shows, for example, often get a new lease on life, or even a brand-new sequel or remake, after making an appearance or two in a Super Robot Wars game. Similarly, the Fire Emblem series was finally brought over to the US to great success after two of its characters made an appearance as unlockable fighters in Super Smash Bros. Melee.
In spite of its recently emerging prevalence, this trope is Older Than Feudalism. The Argonautica by Apollonius Rhodius (3rd century BCE) features nearly every ancient Greek mythical hero all going on a quest to find the Golden Fleece.
Sub Tropes:
The Giant RoboOVA series featured characters taken from several other series Misuteru Yokoyama — the original creator of Giant Robo/Johnny Sokko and His Flying Robot — had written. This included adaptations of the medieval Chinese stories Romance Of The Three Kingdoms and The Water Margins, which led to many main and secondary characters in ancient Chinese clothing coexisting with people in three-piece suits Twenty Minutes into the Future. It also included the very first Magical Girl, Mahotsukai Sally (Sally, the Witch), under her original name "Sunny", as Shockwave Alberto's daughter.
Amusingly, save a select few examples, mostly as cameos, the Alternate Universes are hardly ever populated by actual CLAMP characters, but Alternate Universeinstances of them.
Their first crossover happened in Clamp Campus Detectives since the three main character were in series/stories on their own before CCD: Nokoru Imonoyama in Duklyon, Akira Ijuin in 20 Mask ni Onegai (Man of Twenty Masks) and supposedly Suou Takamura showed up in an old oneshot. Then there was X/1999 where characters from past CLAMP series started appearing, including Subaru, the main character of Tokyo Babylon, as a major character, and during his series set in the early 90s it was said that he would have a role in End of the World as We Know It that is X, making for a bit of foreshadowing.
Before Dengeki Gakuen RPG: Cross of Venus (mentioned below), there was this animated short produced for Dengeki Bunko's 2007 Movie Festival, featuring chibi versions of characters from Kino's Journey, Inukami! and Shakugan no Shana (Note that the chibi Shana here is notShana-tan; for one, she is the stalker rather than said omake series' Kazumi.).
While most Go Nagai series contain cameos here and there, the recent Shin Mazinger seems to be going the whole way. Characters from several alternate versions of Mazinger Z have shown up, as well as characters from Violence Jack (itself, a Deconstruction Crossover) and the titular demon from Mao Dante. Unsurprisingly, this series is being directed by the same man behind Giant Robo, Yasuhiro Imagawa.
Chibi Chara Go Nagai World was a crossover which featured SD versions of Mazinger Z, Devilman, and Violence Jack (with in-story explanations for the characters being SD).
The Pretty Cure All Stars movie series allows the Cures from the past seasons to meet (and be friends with) the new team.
Crisis on Infinite Earths was a massive DC multiverse crossover that attempted to pare down the 837,000 alternate Earths (some populated by the superheroes DC Comics had acquired by buying out other comic book companies over the course of 50 years, others created just to resolve DC's own legendary Continuity Snarls) into one world, obliterating many "Alternate Earth" characters in the process.
Fables is about various figures from fairy tales and folklore living secretly in a neighborhood in NYC.
Planetary is about an investigative super-team in the Wild Storm universe. Their members have had run-ins with Dracula, Sherlock Holmes, Jenny Sparks from The Authority and multiple versions of Batman.
The Indelible Alison Bechdel offered a mash-up of various lesbian and gay comic artists, who threw their characters into the same world for a party. As the mash-up included Diane DiMassa, creator of Hothead Paisan: Homicidal Lesbian Terrorist, the results were hilarious.
Joe The Barbarian does this in a manner similar to The Indian In the Cupboard.
A non-canon Judge Dredd story in the 1980 Dan Dare annual had Tharg bring all the popular characters currently being published in Two Thousand AD as well as the Starlord to Dredd's apartment for a surprise party. Then the robots that actually write the comics went on strike, forcing the characters to beat them all up.
The Alan Moore comic Albion shoves together a whole bunch of British comic characters of varying obsurity, most of whom are imprisoned by the Government as part of The Masquerade.
A recent MasterCard commercial featured several food mascots (from Count Chocula to the Pillsbury Doughboy) eating dinner — with Mr. Clean doing the dishes.
USA Network's commercials play this for laughs, having various combinations of characters from their shows (Burn Notice, Monk, Psych, others) encounter each other and make idle conversation.
Many Seltzer and Friedberg works, such as Epic Movie and Disaster Movie, could be considered Massive Multiplayer Crossovers, insofar as they feature many characters and plot elements (or weak parodies thereof) from recent movies and mash them all together. By all rights, this really should produce something worth watching on some level.
A version of this in Star Trek: Generations, which featured the captains of two Enterprises from completely different eras (Kirk and Picard) in the same film. Star Trek has done this numerous times, if you consider the different series separate entities of the same intellectual property.
Van Helsing, which features the eponymous monster hunter battling Dracula, a werewolf, Frankenstein's Monster, Igor and Mr. Hyde.
And with horror-movie creatures in the Waxwork movies.
Toy Story features many toys from rival companies as major or minor characters including Mr. Potato Head, Barbie, and Legos among many others. (And probably some expies too.)
Kim Newman once wrote a short story about Terry and Bob of the British sitcom The Likely Lads fighting in the Vietnam war with William of Richmal Crompton's old Just William stories and other fictional characters.
Silverlock by John Myers Myers, in which the protagonist A. Clarence Shandon is shipwrecked in the Commonwealth of Letters, where everywhere he goes and everyone he meets is a literary, mythical and/or historical reference.
A fairly extensive list of specific references can be found here.
Robert A. Heinlein's The Number of the Beast features a Time Travel device that does double duty as a portal into The Multiverse, allowing his characters to visit every fictional universe ever, including all of Heinlein's own novels. They coin the term "World as Myth" to describe the Recursive Canon necessary to make this work, and wind up hosting a convention for just about every Science Fiction character ever.
Spider Robinson's Callahan's Crosstime Saloon series - including Callahan's Lady - contains cameos from characters created by crime writer Donald E. Westlake, SF legend Robert Heinlein, and even classic British humourist P. G. Wodehouse, all interacting with each other. (Most likely inspired by Heinlein's The Number of the Beast, mentioned above.)
Simon R. Green's Nightside take place in a secret city under London that's a giant crossoverfest. John Taylor, Green's protagonist, has met characters from all manner of books, movies, television shows, and other assorted places though they are largely referred to in vague, shadowy terms so he doesn't violate the copyrights too badly. There's everything from a Traveling Doctor who had a trick with celery to having to exorcise Kandarian demons from his answering machine to giant 'bears of little brain' that work for the auction house.
For even more fun, representatives from most of Green's other series (the Deathstalker novels, the Darkwood books, etc) show up, waiting around to speak to Father Time.
While Neil Gaiman's short story A Study in Emerald is primarily a crossover between the works of H.P. Lovecraft and Arthur Conan Doyle, it contains subtle hints that characters such as Dracula, Frankenstein, and Dr. Jekyll also exist in the same universe.
And again in Roger Zelazny's book "Roadmarks" where Red runs across a short man with a small mustache whom Red refers to as "Adolph" driving a battered black Volkswagen, and later on in the book he makes a call to someone he calls "Doc", who is described as "A big golden-eyed guy with one hell of a suntan, wearing a torn shirt, and driving a hot little 1920's roadster" which could only have been Doc Savage.
Doc Savage villain John Sunlight also makes an appearance.
Zelazny was a comic book reader and fan. In _Blood of Amber_ Merlin has dinner at Bloody (Last Deceased Owner's Name)'s place—Boody Andy's at the time—while a gent (with a pronounced scar through his eye) eats at a neighboring table and warns Merlin to show a blade so the local roughs get no ideas. "Old John" was clearly John Ostrander and Tim Truman's mercenary John Gaunt (aka Grinner, Grim Jack) from Cynosure, a cross-dimensional city in a multiverse adjacent to Amber. The two roughs did not last the night.
The works of Dr. Seuss were combined into a Broadway musical called Seussical, which mainly takes its story from Horton Hears a Who!, Horton Hatches the Egg, and The One Feather Tail of Miss Gertrude McFuzz, but contains elements and characters from I Had Trouble in Getting to Solla Sollew, The Butter Battle Book, How the Grinch Stole Christmas!, and more. And of course, they have The Cat in the Hat to move the plot around.
Jim Henson's The Wubbulous World of Dr Seuss did something similar, with Yertle the Turtle as a recurring villain.
Stephen King's The Dark Tower series spans across the majority of his prior works.
The Harold Shea series of short stories are about Harold and company visiting various settings taken from mythology and public domain fiction, usually one per story.
Brazilian author Monteiro Lobato took this trope to insanelevels in his kid's books set in the Yellow Woodpecker Farm. The eponymous farm is an interdimensional nexus to, essentially, every fantasy and adventure fiction character ever written, including but not limited to the Greek Gods, Sherlock Holmes, the Neverland people, the Arabian Nights, the fables from Aesop, Grimm, Andersen, the Three Musketeers, medieval Knighs etc etc etc ad infinitum. He even managed to throw in some characters copyright laws didn't allow him to. To top if off, characters native to the series' own universe are not few in number.
Peter David wrote two novels where X-Men characters appeared in the Star Trek: The Next Generation universe.
L. Frank Baum did this in the fourth book of the Oz series, The Road to Oz, by inviting characters from his other books to attend Princess Ozma's birthday party, hoping to get his Oz readers interested in those other non-Oz stories. This included everybody up to and including Santa Claus (as in The Life and Adventures of). The implication, of course, is that every book Baum ever wrote takes place in the same universe as the Oz books.
James A. Owen's Chronicles of the Imaginarium Geographica does this with pretty much every major work of fantasy, history, and real life. It's awesome.
Live Action TV
The "Night of Elizabeth Taylor", broadcast on CBS around 1995-96, saw a diamond necklace lost by Elizabeth Taylor became a common plot element linking four SitComs — The Nanny, Cant Hurry Love, Murphy Brown and High Society — in one massive crossover. It was intended as an embedded advertisement for Taylor's new perfume, Black Pearls.
Disney did a triple-episode MMC with three of its shows. The show was entitled That's SoSuite Life OfHannah Montana, with one classed as a Suite Life episode, one as a Raven episode, and one as a Hannah Montana episode, where Hannah and Raven visited the hotel the twins live in.
Likewise, there's the Wish Gone Amiss triple-episode, except it is more loosely tied together. It all involves the title characters from Cory in the House, The Suite Life of Zack and Cody, and Hannah Montana making a wish on apparently the same shooting star. Each episode has its own method of returning to the Status Quo — Cory gets a literal Reset Button, Zack and Cody's wish was all just Zack's dream, and Hannah returns her life to normal when Jackson unwittingly wishes that the world did not know Hannah's double life.
There's also the WizardsOn Deck with Hannah Montana that goes by the same formula that the That's So Suite Life of Hannah Montanna did, except with the stars visiting the hotel's ship instead of the hotel itself.
Kamen Rider Decade is this in regards to the Heisei era Kamen Rider shows. The main character dimension jumps into alternate universes based on the 9 previous Kamen Rider series of the last 10 years (as well as the canonical universe of Samurai Sentai Shinkenger). Plus, the first movie features every main Rider created before Decade, even ones that only had appeared in one-shot movies previously.
The second movie, a Grand Finale, even includes some postmodern commentary on the "interesting effects on the fiction chosen" mentionned in the opening paragraphs. To quote the original universe Wataru: "The tales of the Riders were something that would be eventually lost to time. But because of Decade's battles, they will remain fresh in people's minds..."
Similarly to Kamen Rider Decade, Kaizoku Sentai Gokaiger is a crossover series. But compared to Decade, in which the main character could only be Riders of the last decade, the Gokaigers can transform into any of the Sentai from the past 34 teams (barring Sixth Rangers - that is, until their own Sixth Ranger joined up). Additionally, while Decade established that every past Kamen Rider was its own universe, Gokaiger establishes that all Super Sentai took place in a single universe.
Perfectly justified that Inazuma Ginga in Sun Vulcan episode 45 was wanted by the Galactic Police. Shozo Uehara who wrote the character would be the main writer of the Space Sheriff trilogy.
The Children's Party at the Palace, a British production broadcast live from Buckingham Palace on June 25, 2006, celebrated Queen Elizabeth II's 80th birthday with a wild romp featuring dozens of literary and TV characters including (among many others) Cruella DeVille, Peter Pan and Captain Hook, Sir Topham Hatt from Thomas the Tank Engine, Wallace & Gromit, the White Rabbit from Alice in Wonderland, Enid Blyton's The Famous Five, Harry Potter, Ron Weasley, Hermione Granger and Neville Longbottom from the Harry Potter movies, and starred the Queen as herself.
The Sabrina the Teenage Witch episode "Inna-Gadda-Sabrina" extended its story through the following three shows that night: Boy Meets World, You Wish, and Teen Angel. Each show was set in a different time period in going with the theme.
It wasn't the first time - in fact, quite a few crossovers spanned the entire TGIF lineup from time to time, and even an occasional though less involving tie-in for all ABC weekly sitcoms during this period.
There was also one that was linked by Steve Urkel. He ends one episode of Family Matters by blasting through the Winslow's roof in a jet pack, and he crashes into the Lambert's roof at the beginning of the an episode of Step by Step where the plot centers around him. I forget if any other shows were connected as well.
A very simple one, but the iStart A Fan War episode of iCarly included characters from Drake & Josh and Zoey 101, helping to fill out the Nick Verse.
In Doctor Who, the climax of the Second Doctor serial The Mind Robber. D'Artagnan vs. Cyrano de Bergerac! Blackbeard vs. Sir Lancelot! Plus Gulliver and Rapunzel on the sidelines.
Law & Order crossed over with Homicide: Life on the Street a few times, until they eventually just decided they were set in the same continuity altogether, to the point of having John Munch, who originated in the latter show, permanently set up shop in the former.
John Munch is a central figure in this Hypothesis.
The Earth Day Special, which aired on ABC in 1990, was a huge crossover featuring just about every pop culture icon from The Eighties in a very bizarre, thoroughly nonsensical plot.
Also in 1990, Cartoon All-Stars to the Rescue, the ultimate Very Special Episode combining well over a dozen Eighties cartoon characters. Aired once and only once, it's full of Narm yet also bizarrely entertaining. Rumor has it that it's never been aired since because Jim Davis claimed he hadn't authorized Garfield's inclusion in the show.
In the CSI: Crime Scene Investigation-verse, the original series crossed over with the Miami series in 2002 to serve as the pilot for the latter; the Miami series then crossed over with the New York series in 2004 to serve as that series' pilot, and the series crossed over again in a two-hour storyline in 2005. The original series also crossed over with Without A Trace in 2007 a two-hour storyline across both series. Following the departure of William Petersen (who opposed the spinoffs and did not appear in any scenes featuring the Miami team in "Cross Jurisdictions"), CBS put together a massive crossover in 2009 spanning all three series that involved the Las Vegas series' Raymond Langston going to Miami and New York while investigating a human trafficking organisation.
The second western MMC took place a year after the first on what seemed to be an ordinary episode of Maverick called "Hadley's Hunters"; during the course of that hour he ran into people from 5 other shows: Lawman, Cheyenne, Bronco, Sugarfoot, and he stops by the office from Colt 45 but nobody was home (a reference to the show being recently canceled).
Strangely he also ran into the parking lot attendant from {{77 Sunset Strip}} which was set in the 1960s — I guess he had an ancestor who lived in the old west.
The Argonautica (a.k.a. Jason and the Argonauts) by Apollonius of Rhodes (3rd century BCE) is one of the very first Massive Multiplayer Crossovers, arranged in what would become a fairly classic method — basically throwing one or two dozen heroes from various separate Greek myth cycles together on a boat with a common mission. This of course makes the Massive Multiplayer CrossoverOlder Than Feudalism.
Many of the same characters also appear in the story of the Kalydonian Boar Hunt - which, Depending on the Author, may occur before or after The Argonautica.
According to some religious studies texts, this has also gone on in many, many other myths: the most notable involve various saints meeting each other. This goes on even today.
There's an updated version. It is as though the internet gave birth.
The Machinima "Beans". Firstly, it crosses over characters from three different series and is made by three different machinima directors, then the storyline involves various internet memes... Oh. And it's made on Super Smash Bros.. Making it a crossover on a crossover.
Stand Up Comedy
There's a Star Trek-related comedy routine in which Mr. Spock, the HAL 9000 computer, and Obi-Wan Kenobi all appear on Jeopardy, in a mental variant of an Ultimate Showdown of Ultimate Destiny. Kenobi is declared the winner, but only because he uses the Jedi Mind Trick on Alex Trebek.
Stand-up comedy troupes sometimes feature a series of comedians who usually headline their own shows:
The Original Kings of Comedy
The Blue Collar Comedy Tour
The Comedians of Comedy
Tabletop Games
The Spelljammer and Planescape settings were designed with this in mind. Spelljammer in particular has rule books dedicated to detailing the Crystal Spheres of settings such as Krynn, Abeir-Toril, and Oerth. Where as Planescape has portals to every type of world imaginable.
Only related through the VS. series via the appearance of one Capcom series rather than multiple but what the heck: Cross Edge is a RPG with Compile Heart at the helm of development. Characters from Darkstalkers, Ar tonelico, Disgaea, Spectral Souls, Atelier Marie and ManaKhemia show up in this one.
There's also Tatsunoko Vs Capcom, which returns to the gameplay of the Marvel series but instead pits the Capcom characters against the works of Tatsunoko Productions like Gatchaman and Casshern. It is basically Marvel vs. Capcom using Japan's Marvel.
Even before Tatsunoko vs. Capcom, there was a Fighting Game called Tatsunoko Fight, which pitted four Tatsunoko superhero anime (and one original made-up anime) characters, along with their females/sidekicks and villains.
crossover not featuring Morrigan, (Anakaris, Demitri, Felicia and Jedah, plus Pyron as one of the final bosses, were the Darkstalkers representants) but also the only game where we were able to fight as one (or two) of the Red Earth characters who aren't Tessa. (Leo, Hauzer, Hydron and Kenji were the representants)
In contrast, the Super Robot Wars series (almost certainly the originator of this trope in video game form) has magnificent, complex plots, and the individual games have touched upon nearly every Humongous Mecha series in existence. Particular of note is how they merge individual episodes to make missions, including having the famous "dancing" episode of Neon Genesis Evangelion set on Macross Island.
Chaos Wars uses a similar SRPG system to Super Robot Wars, but instead has more typical JRPG heroes from Atlus, RED, Idea Factory, and Aruze. This doesn't sound all that impressive — outside of Atlus and maybe Idea Factory those companies are virtually unknown in the States, until you realize this includes Shadow Hearts (Aruze), Growlanser (Atlus), Spectral Souls (Idea Factory), and Gungrave (RED). A sequel has been talked about, and there are hints that Shin Megami Tensei/Persona characters may make it in, and that Nippon Ichi might be invited to join the other 4 designers in the next series.
And ditto Trinity Universe, which will have two story modes — one with Nippon Ichi (Disgaea) characters, and one with Gust (Atelier Series) characters. It apparently revolves around someone throwing trash into Laharl's back yard. Gust and NIS are making a habit of doing these crossover games — NIS also has a habit of localizing all of Gusts' releases in the states, too.
Super Smash Bros. has a number of first- and second-party Nintendo characters fighting each other - and the third iteration of the series, Super Smash Bros. Brawl, has taken it a step further, including Solid Snake from Konami's Metal Gear games and Mario's longtime rival, Sega's Sonic the Hedgehog.
There are also various fanmade Smash Bros. clones, then most notable example being the Super Smash Flash series for its inclusion of more third-party characters and anime characters.
Square-Enix's Kingdom Hearts series merges nearly every movie in the Disney Animated Canon and some outside of it with the feel and characters of the Final Fantasy series (though, just like the Tsubasa example above, the Disney characters are alternate universe incarnations, as implicitly stated in the TRON world).
On the PSP is Dissidia: Final Fantasy, where heroes and villains of various Final Fantasy games face off as part of the machinations of two opposing powers.
Tales of the World, Namco's set of Massive Multiplayer Crossover games for their Tales Series. One bonus, though, is that the Narikiri Dungeon heroes' ability to dress as any Tales character and gain their abilities applies to bosses, too. Now add in the fact that theme music changes to whatever character or costume is in the lead of a party in battle, and you have a winning idea when a Tales fan can battle to Motoi Sakuraba's more popular themes, like Fighting of the Spirit or Decisive.
A recent download introduces Taki and Mitsurugi from Soulcalibur for use as well.
Similarly, there is [[Dynasty Warriors: Gundam]] that has several stories focusing on different pilots teaming up into two forces because of this. Eventually, you can even have different pilots using different mecha.
Similarly, Battle Stadium D.O.N. is the same, but specifically has characters from Dragon Ball, One Piece, and Naruto (hence the D.O.N.).
Speaking of which, Shounen Sunday and Shounen Magazine are looking to take a bite out of Jump Super Stars together with Sunday VS Magazine Shuuketsu Choujou Daikessen (Also known as Sunday vs. Magazine) on the PSP.
Quake III (and by extension, Quake Live) included the Doom guy, the Quake marine, the Quake II marine and the guy from Wolfenstein 3D (named Sarge here) among other characters as playable characters. Of course, they were all of the Silent Protagonist variety to begin with, so this didn't make a huge difference.
The mod Generations Arena takes the above concept and runs with it, extending the crossover to the gameplay via five classes, each adapting the gameplay of said five games to the Quake III engine, right down to the finest details. Doom's fast-paced battles and BFG against Quake's flexible air control and powerful rocket launcher? You got it.
And that's not even including custom skins, with which the crossovers skyrocket through the roof.
M.U.G.E.N is a customizable 2D fighting engine that permits end users to homebrew reproductions of any other character in the entire genre, and create unique ones. Fighters already exist for every "vs" title released and almost every fighting games, and can be crossed over in unique ways.
Nippon Ichi has recently released a new one in Japan with a release coming in summer 2010 to the US, Trinity Universe. It's made in conjunction with Gust and Idea Factory.
In theory, expansions or further installments could potentially include characters from just about any video game you could name (in practice, any character owned by a company too chicken to go in on a project solely on the basis that it's a cool idea can be struck from the list).
Any Wii game that uses Miis as playable characters or NPCs can become this if you make enough of them.
The Macross Frontier PSP game series allows you to play all Macross universes. The recent title, Macross Triangle Frontier, covers Macross Zero, Macross (as well as Do You Remember Love), Macross Plus, Macross 7, Macross Dynamite 7, Macross Frontier (as well as Macross Frontier: The False Songstress) and Macross 2.
In a more literal example, Minecraft allows anyone to make their own character skins, which leads to 20+ characters all working together to build a house/civilisation and mine for diamonds.
Cartoon Network: Punch Time Explosion is a Smash Bros. clone with Cartoon Network characters. (BTW, it's not a clone just because it's a crossover either. It literally has the same gameplay, right down to tilt/smash attacks, Final Smashes, assist characters, and the percantage point system.)
Though it never crossed over with both at the same time, It's Walky!! had crossovers with both Melonpool and Fans!! that established both as part of its universe (or multiverse in the latter case) and which ended up having a lasting impact on its storyline.
Kevin & Kell and General Protection Fault had an arc where two GPF characters wandered into K&K's Domain world. The artists managed to work the events into both their storylines that were running at the time, and apparently drew a strip each day—both had two-strip days where the storyline advanced.
Starslip Crisis: Alterverse War is a mashup of a large number of science fiction webcomics, and had just started as of October 2007.
Choo-Choo Bear hired the Pet Professional from the webcomic of the same name to kill his homicidal cousin Twitchy-Hug.
And recently Davan from S*P has been seen texting with Candy from ''Girls with Slingshots'' after running into her at the wedding of Jameson and Maureen.
Choo-Choo Bear later had kittens with Sprinkles of Girls with Slingshots, one of whom Davan gave to Roz of Shortpacked!, and another is by Hazel to her cousin Robyn from All New Issues.
Even better, none of those strips have been shy about crossovers of their own. QOW drags in Punch And Pie, which stars its Breakout Character Angela; It's Walky pulls in Fans! and Avalon.
Questionable Content has crossed over with Diesel Sweeties, which has itself crossed over with Scary Go Round. Questionable Content has also crossed over with Applegeeks, which, having crossed over with Ctrl+Alt+Del, would turn the whole group into one quasi-incestuous ball of webcomics. I'm reasonably certain that PvP has been referenced in at least one of these, probably Diesel Sweeties, and since the former has crossed over with Penny Arcade more than once, it's completely cross-eyed insane over there.
And the Author of Ctrl+Alt+Del exists as a person in the Penny Arcade universe, so that means, if you follow the little red thread of universal strings, that he exists in the same plane of existence as his characters..
Don't forget that Applegeeks had a major crossover (well, on its end) with Megatokyo at one point. Which chains the whole thing to a specific date, making things even crazier.
It gets better. Questionable Content is now having background extras as characters from other comics like Girls with Slingshots, Octopus Pie, Anders Loves Maria and Overcompensating. Since Overcompensating features the author and most people known in the webcomic industry, it means all these characters now exist in the same universe as their creators.
The cast of Shortpacked has visited the Coffee of Doom coffee house from QC on occasion, including once when both artists did a take on the samescene. Combine that with the S*P Intercontinuity Crossover Nexus mentioned above, along with all their respective crossovers, and we have a massive webcomic universe that could give Marvel a run for its money.
Sluggy Freelance hosted one of these during the Filler Arc "Sluggy Freelance: Where Are You?" When all of Sluggy'sactors are kidnapped (a.k.a. Pete Abrams decides to take some time off) characters from several other webcomics are hired to fill in for them and/or find the kidnappers.
Least I Could Do recently finished the Ultimate Final Civil War Invasion Crisis Thing, which featured the gaming webcomic characters trying to kill the slice-of-life comic characters. (The Order of the Stick, meet xkcd.)
Ménage ŕ 3 and Sore Thumbs crossed over at some point and are implied to be in the same universe, and Ménage ŕ 3 crossed over with School Bites. If this keeps up we'll wind up with every webcomic crossing over to one another.
The writer of No Rest For The Wicked footnotes her comics so you can get all the fairy tales she's using characters from.
Although there are many similarly-themed RPs, Milliways Bar deserves mention just for its size. The basic premise is that any character from any fandom can find themselves at the titular bar... and sometimes it seems like just about everyone has.
The Game in which Life In A Game takes place seems to take all video games as true, with Zelda appearing alongside Master Chief, and Frog serving as the hero's Jerkass Mentor.
Ask That Guy: (speaking to the various reviewers present) In fact, I think there's a lot of you who want to do crossovers, aren't there? Because everybody really eats that shit up.
Everybody: Yeah!
All the cast stayed in Chicago for a couple more days to film crossovers after this. Highlights include Linkara being force-read his own Massive Multiplayer Crossover fanfiction by the Sage, the Ultimate Warrior writes a comic series so bad that reality breaks down and Linkara and Spoony keep changing into different Alternate Universe selves and the Critic and Nerd joining forces to review... a Making Of of a Teenage Mutant Ninja Turtles Tour. Yeah.
Later on when faced with Uwe Boll's Alone in the Dark, the Nostalgia Critic gave up on reviewing it. Until! Spoony and Linkara arrived to assist him.
The Two Year Anniversary is another huge crossover event. And in turn, it allowed some once-in-a-lifetime crossovers as by this point, quite a few reviewers are from around the world.
In 2011, things repeated. Y Ruler of Time used MAGFest to do another multiple reviewer crossover (The Last Airbender, with Todd in the Shadows, Jesu Otaku and Rollo T, plus various cameos). And Year Three had a crossover series and various individual joint reviews (Todd even opens his one saying that the trip means crossovers... and gets shot down by three people before Film Brain accepts to watch a movie with him).
How about TheUltimate Showdown of Ultimate Destiny flash video? Good guys; bad guys; explosions as far as the eye can see. Way too many pop culture icons to count.
Disney owns all the characters it uses plus a whole network. The most recent example is House of Mouse, which has Mickey and Co. as hosts of a nightclub/theater, with the characters of the feature films as the audience.
Much earlier, in 1972, the one-off animated special The Man Who Hated Laughter united all of King Features' popular characters — meaning not only Flash, the Phantom, Mandrake, and Lothar, but also the likes of Popeye, Blondie, Snuffy Smith, and Beetle Bailey.
