In the aughts, it seemed like every network wanted to jump on the crossover train. For example, Disney popularized the children's sitcom crossover with specials like, "That's So Sweet Life of Hannah Montana" and "Wizards on Deck with Hannah Montana." However, no other network could animate battle royales and cartoon crossover adventures quite like the cartoon juggernaut, Cartoon Network.
Since the turn of the millennium, Cartoon Network has produced some of the most iconic crossover episodes ever to grace the small screen. Shows like The Grim Adventures of Billy and Mandy and Ben 10 were network staples before their cross-program specials brought them into the greater CN universe. They've since further cemented themselves in cartoon history. However, they're not the only ones.
10 Finn and Jake Meet a Very Familiar Blue Jay in "Ketchup" (Adventure Time)
In this season nine episode of the Cartoon Network classic Adventure Time, BMO and Marceline catch each other up on their respective recent adventures. Following the conclusions of the "Stakes," "Islands," and "Elements" miniseries, BMO opens the episode with a creative retelling of the events of the "Islands" arc.
In this segment, the first of three animated by guest animators Alex and Lindsay Small-Butera, BMO recalls having come across a particular blue jay on his travels with Finn and Jake. This is obviously a reference to Regular Show's Mordecai. The creator of Regular Show and voice of Mordecai, J.G. Quintel, provided the voice behind the blue jay's signature "Ohhh!" for the brief cameo.
9 Ed, Edd n Eddy Look For An Imaginary Friend in "Eddie Monster" (Foster's Home For Imaginary Friends)
Foster's Home was a 2000s fan favorite amongst children and their parents for its bright colors, wacky characters, and intelligent humor. By the end of the show's run, it was notorious for referencing other popular shows at the time, including brief appearances by characters such as The Powerpuff Girls' Mojo Jojo, and Re-Animated's Golly Gopher.
In the season three premiere, "Eddie Monster," Ed, Edd n Eddy's main trio is briefly seen standing beside Dexter's Laboratory's titular vaguely-European scientist. While the four only appear for a moment, their cameos are among the most memorable of the network's many crossovers.
8 "The Grim Adventures Of The Kids Next Door" Proves Exactly Why Grim Doesn't Like Kids
This half-hour special sees the titular Kids Next Door come to Endsville to save Billy from a case of tattered pants. Once the kids of Sector V arrive to help Billy, the dark and mysterious Delightful Children from Down the Lane also make an appearance, hoping to "delightfulize" the children of Endsville.
By the episode's climax, Billy has accidentally fused himself, the Delightful Children, and Grim's scythe together to form a Frankenstein's monster-esque "Delightful Reaper," while Mandy has taken over and renamed the KND. The special comes to a dramatic close as Grim and Numbah 1 team up to defeat the Delightful Reaper in a classic giant monster battle á la Godzilla vs Mothra.
7 Steven Universe Learns A Valuable Lesson From Uncle Grandpa in "Say Uncle"
Despite less-than-favorable reviews from fans, the Steven Universe and Uncle Grandpa crossover special "Say Uncle" is an incredibly memorable episode for both shows. The season two episode of the Steven Universe sees Uncle Grandpa and his entourage attempting to aid Steven in summoning his magical shield – with little success.
It isn't until the Crystal Gems ambush him on the beach, annoyed at Uncle Grandpa's dangerous and reckless attempts to help Steven, that he's finally able to summon his shield. Although the episode isn't considered canon in either show, it still offers a fun, lighthearted adventure perfect for casual viewing.
6 Uncle Grandpa Hosts The Star-Studded "Grampies"
Yet another Uncle Grandpa crossover, this short, which came at the end of the season three episode "Pizza Eve," brought Cartoon Network royalty to UG's Grampies' stage. The short sees Uncle Grandpa hosting a Grammys parody for characters of various popular Cartoon Network shows, only for the show to be rigged in favor of the Mr. Men Show cast.
In the tradition of Cartoon Network crossovers, everyone's favorite characters are seen sitting with each other in one grand, yet brief, crossover in "The Grampies." Adventure Time's Finn and Jake, the Powerpuff Girls, Samurai Jack, and Ben 10 are all in attendance, alongside a myriad of other iconic CN characters.
5 "Bravo Dooby-Doo" Brings Together Two Hanna-Barbera Powerhouses (Johnny Bravo)
This season one episode of the '90s classic Johnny Bravo sees Johnny running into the Scooby-Doo! Mystery Inc. gang when his car breaks down on the way to his aunt's mansion. After the gang discovers Johnny's aunt's home may be haunted, they agree to go with Johnny to investigate the mansion.
In classic Scooby-Doo style, a chase ensues between Johnny, the Mystery Inc. kids, and the mansion's resident Ghostly Gardener. It's later revealed the 'ghost' gardener is Johnny's aunt Jebedissa Bravo herself, having donned the disguise to scare away her nephew, who she saw as an embarrassment to the Bravo family.
4 Ben 10 Prepares For An Interdimensional Family Reunion in "Alien X-tinction"
Crossovers don't always have to happen between entirely different franchises. Some crossovers, like Ben Gen 10's "Alien X-tinction" special, bring together different versions of the same show.
This special sees an alternate universe Grandpa Max chasing down the mysterious Alien X across dimensions, running into both the reboot and original versions of the Tennysons and their older counterparts. The various Bens, Maxes, and Gwens band together to take down Alien X before returning to their home universes.
3 Ben 10 and Generator Rex Are Two "Heroes United" In A 2011 Crossover Special
In this two-part crossover special, Ben Tennyson comes to New York City after falling through a rift in the sky. Episodes ten and eleven of Generator Rex's third season follow Ben and Rex as they meet, battle, and subsequently work together to defeat an elusive red mist stalking them and their friends.
The red mist is revealed to be the Alpha Nanite, a mechanical entity created by Rex's older brother Caesar as a part of the Nanite Project. The entity hopes to find an organic host body as its makeshift robotic host is too unstable, but it fails thanks to the combined efforts of Ben and Rex.
2 "Crossover Nexus" Forms A Whole New Superhero Team (OK K.O.! Let's Be Heroes)
"Crossover Nexus" is the most recent of Cartoon Network's large crossover specials, featuring three of the network's most iconic heroes fighting alongside K.O. After finding himself transported to a mysterious and dissolute world inhabited by the captured characters of other Cartoon Network shows, K.O. runs into and befriends Steven Universe's Garnet, Ben 10, and Teen Titans Go's Raven.
The heroes realize the villain, Strike, brought them to this world to turn them into stone. It's the same for other CN characters they come across in an abandoned building later in the episode. They try to escape and fail before deciding to band together to defeat Strike. This special proves how Cartoon Network is nowhere near losing its touch in the crossover game.
1 Aliens Attack In The 2007 Crossover Event "Cartoon Network Invaded"
In perhaps Cartoon Network's biggest cross-program special, "Cartoon Network Invaded" brought an alien invasion to five classic CN shows in a series of special episodes. Foster's Home for Imaginary Friends, Ed, Edd n Eddy, My Gym Partner's a Monkey, Camp Lazlo, and The Grim Adventures of Billy and Mandy were all a part of this extraterrestrial crossover.
Though the event was originally sponsored by Kraft Cheese, the company backed out of the sponsorship at the last minute, leaving board members displeased and their time seemingly wasted. However, the event proved a major success for the network and later went on to become its most memorable crossover yet.