Massive Multiplayer Crossover / Western Animation

• Disney has a long history of putting loads of their characters in the same universe. The most famous animated example would have to be House of Mouse, which sees Mickey Mouse and his friends as hosts of a nightclub venue, with characters from Disney's animated features as the audience.
  • Speaking of Disney, their Chibi Tiny Tales and Chibiverse cartoons feature Super-Deformed versions of characters from their movies, cartoons, and live action shows interacting with one other, ranging from Phineas and Ferb and The Owl House to Halloweentown and High School Musical.
• Many classic Hanna-Barbera characters have been used across the board, in shows like Laff-A-Lympics and Yogi's Gang; this is still done, but with a more satirical bent (e.g., Harvey Birdman, Attorney at Law). The largest gathering of characters, however, came with the Hanna-Barbera 50th anniversary special in 1989 as all the characters gather together to pay tribute. This doubles as Roger Rabbit Effect as they interact with Joe and Bill themselves, along with special hosts Tony Danza and Annie Potts.
• Nearly all recent Warner Bros. animated television series made references and overt cameos with one another.
• The early-1990s public service announcement Cartoon All-Stars to the Rescue had characters like the Teenage Mutant Ninja Turtles, The Smurfs, Winnie the Pooh, the cast of DuckTales, and many others team up to teach a single kid about the dangers of drugs and save his sister from same. Although, if you can see Smurfs, there's a good chance that you're tripping balls already.
• The 1980s cartoon Defenders of the Earth starred King Features' most famous adventure-hero characters: Flash Gordon, The Phantom, and Mandrake the Magician (along with his sidekick, the strongman Lothar).
• 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.
• Captain N: The Game Master featured a mishmash of characters who appeared on the Nintendo Entertainment System done wrong. Most of the episodes took place in the neutral Videoland, with characters like Simon Belmont, Mega Man (Classic) and Kid Icarus Pit hanging around, even if In Name Only. Link and Zelda from The Legend of Zelda (cartoon) appeared too.
• The Children in Need music video "Peter Kay's Animated All-Star Band", which features nearly every significant British Stop Motion characters with a few 2D British and American characters broadcast "live via satellite", including Roary the Racing Car, Fifi and the Flowertots, The Wombles, In the Night Garden..., Angelina Ballerina, Scooby-Doo, Bagpuss, Bob the Builder, Ben 10, Thunderbirds, Postman Pat, Spongebob Squarepants, Fireman Sam, Camberwick Green, Thomas & Friends, Pingu, Teletubbies, The Sooty Show, The Koala Brothers, Peppa Pig, Rubbadubbers, and Paddington amongst others.
  • All singing parts of the characters by their original voice actors. The video took two years to produce, and it's for charity.
• Done with advertising mascots in the short film Logorama. It won the 2009 Oscar for Best Animated Short.
• The Rosey And Buddy Show, a 1992 TV special produced by Nelvana, featured not only animated versions of Roseanne and Tom Arnold, but also the Care Bears, Beetlejuice, Tom & Jerry, Droopy and even Wile E. Coyote's stunt double.
• Aardman Animations made a Google Chrome commercial for Christmas 2012 that featured Wallace & Gromit making a conference call with Ginger, Captain Cuddlepuss and Trixie, the robins, Shaun's flock, and Piella and Fluffles.
• The Uncle Grandpa short "The Grampies" is an award show for Cartoon Network stars be they from classic shows like Dexter's Laboratory, Johnny Bravo and Foster's Home for Imaginary Friends, or currently airing shows like Regular Show and The Amazing World of Gumball. There were even voiced cameos from Steven Universe, Jake the Dog, Belson, and Reboot!Buttercup, mostly complaining about how Uncle Grandpa is winning every award.
• The OK K.O.! Let's Be Heroes episode "Crossover Nexus" has K.O. team up with Ben 10, Garnet, and Go!Raven to take down the villain Strike, who has been taking down heroes from across the Cartoon Network multiverse. This includes, but is not limited to: Hi Hi Puffy AmiYumi, Sym-Bionic Titan, Dexter's Laboratory, I Am Weasel, Mighty Magiswords, The Amazing World of Gumball, Uncle Grandpa, Secret Mountain Fort Awesome, Regular Show, Adventure Time, The Grim Adventures of Billy & Mandy, Chowder, Time Squad, Foster's Home for Imaginary Friends, Ed, Edd n Eddy, Whatever Happened to... Robot Jones?, Courage the Cowardly Dog, Sheep in the Big City, We Bare Bears, My Gym Partner's a Monkey, Squirrel Boy, The Marvelous Misadventures of Flapjack, Apple & Onion, Craig of the Creek, Clarence and Over the Garden Wall.
• The Animaniacs revival does this with reuniting the Looney Tunes, the Tiny Toons, characters from Hanna-Barbera and ever-flippin' Loonatics.
• [adult swim], in 2003, had a New Year's Eve special that united all of their original properties at the time for a series of crossover shorts called "The Bashingtons" with the framing device of Brak's family from The Brak Show inviting all the other [adult swim] characters over for a New Year's Eve party. However, it ended with The Brak Show being officially canceled and Brak naturally being rather upset about it. The last bumper was Brak crying about being canceled as George Lowe (the voice actor for "Dad") complains about his inability to find work.

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