Crossover Alternate Universe

Crossovers. Everyone loves them but they're not always the easiest thing to do. Especially if some storylines are so serialized that there's no wiggle room to allow for crossovers. So what is an author to do? Create an Alternate Universe for the crossover.

This usually takes four main forms:

• Property A is a single ongoing timeline, while Property B isn't. As a result, a version of Property B's basic story, made to fit Property A's timeline, will be utilized. This is the most common and is seen in both official publications and fanfictions. It's important to note that if this is the case, then this trope only applies to Property B.
• Property A followed the canon timeline, up to a point, before it diverged into something that would generally make for a more interesting crossover. Normally found only in fanfictions.
• The characters from Property A are Public Domain Characters and the stories can be altered whatever which way the author wants. For example, if Optimus Prime meets Merlin, expect Merlin to have his story altered before Optimus does.
• Or both stories are so tightly serialized that it's best to just to create Broad Strokes versions of both stories and simply set them in one Shared Universe.

Mind you, a self-contained crossover that a fan wrote between two, or more, properties isn't this. That technically qualifies as an Alternate Universe Fic mixed with Canon Welding (for example, saying that the Time Lords learnt about Time Travel from the Time Stone).

Examples of Crossover Alternate Universe include:

Comic Books

• Believe it or not but the early publications of both Marvel and DC Comics were envisioned as independent anthologies before the Avengers and the Justice League were born. Yes, two of the longest ongoings are Crossover Alternate Universes.
  • Any licensed crossover between the two is likely to also employ this.
• While most of IDW Publishing's crossovers make use of an Interdimensional Travel Device, their Transformers crossovers often take place in micro-continuities, unconnected to the main ongoing story.
  • Star Trek vs. Transformers plays the first option perfectly straight. As Star Trek has never really used micro-continuities and Transformers has had several Continuity Reboots, the writers just tweaked the 1980s adventures of the Autobots and Decepticons to fit with Star Trek's Alternate History.
  • Transformers/Ghostbusters follows suit, taking place in the main Ghostbusters timeline but altering the backstory of the Transformers to fit.
  • Transformers vs. The Terminator has this for both franchises. While this happens all the time for Transformers, Terminator's timeline is such a massive Continuity Snarl that the writers promptly ignored all but its most basic aspects (T-800 travels to 1984 and meets Sarah Connor) and made a new one.
  • My Little Pony/Transformers outright opens with a vendor telling Quibble Pants (a Comic Book Guy-esque pony), and the audience, that this is in play and to not worry about continuity, just have fun.
• Both of Boom! Studios's Mighty Morphin Power Rangers crossovers (one with The DCU and the other with the Teenage Mutant Ninja Turtles) are totally unconnected to the main timeline. The same goes for both other properties, the former seems to be broadly inspired by the DCAU while the latter takes place in a world where both the Rangers and Turtles co-exist.

Fanfiction

• Conquest sees the second option. The backstory diverged from the old Star Wars Expanded Universe when Han and Leia died which led Anakin Solo to reform The Empire because... well The Empire vs The Federation is a good deal more interesting than watching the New Republic peacefully negotiate with the Federation. As a result of Imperials in the Milky Way, the story diverges from canon sometime after Star Trek: Insurrection.
• Happens constantly in Transformers crossovers because, as said above, all the Continuity Reboots on the franchise lets authors get away with this. If the official powers can do it, then why can't the fans?
  • Generally inverted with Transformers Animated crossovers. Since that show takes place in the 22nd century, it's the other properties that get bent around.
• The Tarzan/Lion King/Jungle Book fanfic Two Brothers Under the Sun adheres to the last form.

Film

• Spider-Man: Into the Spider-Verse creates a new universe, the main one, so that other properties of Spider-Man, or Broad Strokes adaptations of those versions, can play around together in.

Live-Action Television

• The Star Trek: The Next Generation episode Parallels sees Worf shunted through several universes, never to be seen again, and all created solely for this episode.

Video Games

• Maybe for Lego Dimensions. Certainly Batman didn't show up to save Gandalf in The Fellowship of the Ring but there is enough ambiguity going on that, due to a Timey-Wimey Ball, Lord Vortech's defeat may have undone the changes to all the universes.
• Injustice: Gods Among Us takes place on one of the many alternate worlds in the DC multiverse.
• Marvel vs. Capcom takes place on Earth-96169.

Western Animation

• The sixth episode of 3Below takes place in a timeline where the Royals meet the Trollhunters long before they normally should along with The Unmasqued World occurring a lot sooner.
• No-Watch Ben's world in Ben 10: Omniverse. Doesn't appear ever again, it's just a place for a handful of Ben's multiversal counterparts to beat the tar out of each other.