Nicktoons Unite!

Nicktoons Unite! is the friendship between SpongeBob SquarePants, Timmy Turner, Jimmy Neutron and Danny Fenton from the SpongeBob SquarePants, The Fairly OddParents!, Jimmy Neutron and Danny Phantom fandoms.

Canon
SpongeBob, Timmy, Jimmy and Danny are the protagonists of their respective shows. All of their shows were airing new episodes in the early-to-mid 2000's.

Nicktoons Unite! (2005)
SpongeBob first meets the other three when following Jimmy's robot dog Goddard through a portal. There, he is suited to survive on land by one of Jimmy's inventions, allowing him fight alongside his new friends. Jimmy explains that one of his inventions allowing multiversial travel has been stolen by his arch-enemy, Professor Calamitous, who used it to team up with the heroes own arch-enemies in a plot to steal the energy of each other's worlds. Entering Danny's hometown, Amity Park, the heroes are swiftly captured by Danny's arch-enemy, Vlad Plasmius, who imprisons them in the Ghost Zone Prison. Danny leads his friends out of the Ghost Zone and defeats Vlad by possessing the body of his father, Jack Fenton. Using another one of Jimmy's inventions, the heroes travel to Bikini Bottom where they meet SpongeBob's friend Sandy who tells them to find his other friend, Patrick. However, Sandy is captured, leading to the heroes having to rescue her and ending up on the Flying Dutchman's ship. Danny convinces the Dutchman to let them go, allowing them entry to the Chum Bucket where they rescue Patrick and prepare to battle Plankton. After defeating Plankton and rescuing Mr. Krabs, he tells them that the villains are stealing energy to power a Doomsday Machine. The heroes then travel to Dimmsdale to fight Timmy's arch-enemy Mr. Crocker, who has infiltrated Fairy World. Returning to Jimmy's lab in Retroville, the heroes realize that Professor Calamitous has been spying on them the whole time, using his shrink ray to hack into the professor's "spy flea", Jimmy is able to locate his lair. Defeating all four of the self-entitled Evil Syndicate at once, SpongeBob renders the Doomsday Machine harmless by unplugging it and Jimmy gives his allies a way to communicate should a new threat arrive. They then return to their respective worlds.

Battle for Volcano Island
The four heroes, alongside a few of their friends, were chosen by the Wise Old Crab to aid the crabs in their battle against their enemy "The Mawgu". However, due to the summoning being interrupted, "the chosen ones" are scattered all across the Volcano Island, with only SpongeBob and Danny being able to stick together. The Wise Old Crab tells them that they were chosen because they were the only ones who could counter the Mawgu's corrupting influence, sending them off to rescue their friends. Alonside the original four, Sandy, Patrick, Squidward Tentacles, Sam Manson and Tucker Foley were also among the chosen ones, with Jimmy not being able to help his friends directly since he was the only one who wasn't summoned properly and is content with staying in his lab, aiding his friends through communication devices instead. Jimmy reveals that the Mawgu is once again sucking energy from their worlds, which would mean the end of the multiverse if it continues uninterrupted. Teaming up, the heroes are capable of draining the Mawgu from his power, leaving him trapped in a rift. After being congratulated by the Wise Old Crab, Jimmy opens portals for his friends to return to their own worlds.

Fanon
Despite getting mixed reviews from critics, the Nicktoons games are very popular with fans of the cartoons, if only because they allow for all of their favorite characters to interact.

Though later games in the series introduce other Nicktoons, most fanwork focuses on the main four. There are a few pieces of fanwork focusing on a "B-Team", consisting of the other characters playable in the series (Jenny Wakeman, Dib, El Tigre, CatDog, etc.). It's not as popular as the main four as there is little of an established dynamic and most of these shows being cult classics instead of the mainstream hits the main four consists of.

A common joke is that Danny is the closest thing to an adult in the group, having to watch over two little boys and an aquatic manchild. People tend to complain the most about any of the main four not being playable, lamenting the removal of a playable Jimmy in Volcano Island and the complete absence of Timmy in Globs of Doom.

A common notion among fans is that the games really should've been TV movies, arguing that though the interactions between the characters are fun and the plots are decent, the gameplay is completely unremarkable.

Fandom
FAN FICTION

Trivia

 * The Fairly OddParents! is the only one connected to all three of the other fandoms:
 * A human SpongeBob has a five-second cameo in the episode "App Trapped!"
 * There were three crossovers with Jimmy Neutron: Boy Genius, called "Jimmy Timmy Power Hour". Those also spawned their own ship.
 * FOP and Danny Phantom share a creator, artstyle, artists and writers. Numerous references to each other imply that they share a world.

Variations

 * DanBob for the friendship between Danny and SpongeBob
 * Hartman Bros for the familyship between Danny and Timmy
 * JimmyTimmy for the ship between Jimmy and Timmy
 * Spooky Nerds for the friendship between Danny and Jimmy