One of the hallmarks of obsessive fandom is the crossover combat “what if” scenario, pitting two iconic characters from different universes against one another. The set ups can vary, but it’s generally accepted that you shouldn’t presume scenarios that are tailored to one character’s strengths.
Why Do We Do This?
There are a lot of reasons for this phenomenon. First and foremost is fan passion. No matter how prolific a creator may be, any franchise eventually runs out of source material to consume. Fans want more. They aren’t done thinking about the characters, the setting, the premise. They set off exploring it on their own, or with like-minded fans. Of course, put any two die-hard fans together for long enough, and they’re going to find points of disagreement, especially when discussing two fictional universes in the same conversation.
That brings me to the second point: mental exercise. There is an undeniable (for geeks anyway) fun in analyzing a fictional world and its fictional inhabitants and comparing one to another. Exactitude is rare in fiction, with most limits and abilities inferred or extrapolated from what is shown by the creator. Within the same universe, comparisons are often guesswork. Between two (or more) different universes, it’s comparing apples and oranges … as seen through a telescope … and the oranges are actually part of a wax display. The analysis is objectively impossible, rationally precarious, and utterly irresistible. It can provide years of entertainment, and never be resolved. It is the everlasting gobstopper of debate topics.
Who Gets Chosen?
The short answer: everyone.
The longer answer: Generally iconic characters from major franchises, usually the ones who are deemed to be most capable in a fight. Comic book characters are ripe for the picking. I let Google’s auto-complete feature loose on the “Who would win a fight between …” search, putting a starting letter for the next word in the search. Most of the popular searches were comic book characters, especially ones who have also starred in movies.
As for pairings, it’s often a like-versus-like crossover. A brutish warrior from one world against a brutish warrior from another. Wizard against wizard. Martial artist against martial artist. God versus god. Usually it involves two characters who fill the same niche in their universe. Often this is done between rival factions of fans, each hoping to prove their universe boasts the best warrior/wizard/god/monster/what-have-you.
How is a Winner Determined?
Ooh, this is a sore subject. If this was easy, it wouldn’t be so much fun for those involved. If it got resolved, it would be over (not for everyone of course; some would fight “the good fight,” disputing the results). Sometimes fans will concoct elaborate thought experiments, pulling facts and examples from one fictional universe and trying to apply some degree of scientific rigor to the process. Once in a while, creators will collaborate to answer (or at least explore) these questions. Alien vs. Predator and the Marvel vs. Capcom games are attempts to both address this phenomenon and cash in on it.
However the dirty little secret of this entire concept is this: The winner is whoever the one writing the fight wants it to be.