Generally, video game characters stay in their own little worlds. Mario and his crew tend to stay in Nintendo's world. The characters from Mortal Kombat don't fight Street Fighter characters.
However, the companies that make video games sometimes come together for some very interesting crossovers. Sometimes, these characters come together and make complete sense. But for every sensible crossover, there are some pretty crazy ones.
In fact, there are some video game crossovers that are so crazy that you might not believe us that they exist until you actually play them yourself.
1. Mario & Sonic at the Olympic Games
This one is actually a trifecta of weird video game crossover. Pitting Mario and Sonic against each other is pretty strange, seeing as they were two characters who defined the competition between Nintendo and SEGA for multiple console generations. But what really makes it weird is the mixture of the Olympics. It's not some imaginary video game Olympics. Nope, it's Mario, Sonic, and a bunch of their friends competing at the real-world games. It's weird. It makes so sense. It's awesome.
2. Battletoads & Double Dragon
Battletoads and Double Dragon were two games that were actually competing for beat-em-up supremacy back in the day. Then, as if from out of nowhere, Battletoads & Double Dragon brought the anthropomorphic toads together with Billy and Jimmy from Double Dragon. The gameplay errs more on the Battletoads side (it's soul-crushingly difficult), so if you decide to go back to it, be prepared to suffer.
3. Kingdom Hearts
The entire Kingdom Hearts franchise is a giant, weird crossover between the world of Final Fantasy and Disney. Somehow, Disney and Square Enix managed to come together to create one of the most beloved video game franchises by throwing together two things that seem like complete opposites. Maybe it's what happens when you actually get a magnet to connect on the same poles.
4. Super Smash Bros.
The first few games in the Super Smash Bros. series weren't all that weird in terms of crossovers. Sure, seeing Samus in Mario in the same game was a little weird, but things really took a turn for the strange when characters from outside the Nintendo multiverse came in. For me, the whole thing became insane with the introduction of Solid Snake as a playable fighter. The deadly serious espionage soldier fighting in a goofy platform fighting game makes no sense... And we love it!
5. X-Men vs. Street Fighter
This one doesn't seem so weird now with the popularity of the Marvel vs. Capcom games but at the time, X-Men vs. Street Fighter was an insane idea. Having Capcom's beloved roster of fighters take on Marvel's huge crew of superheroes and villains seemed like an impossible dream. Not only did the crossover succeed, but it led to tons of sequels and other crossover fighting games including Capcom vs. SNK, Street Fighters X Tekken, and tons of others. This cross truly was a game-changer.
6. Mortal Kombat vs. DC Universe
While not as revolutionary as X-Men vs. Street Fighter, the characters of the Mortal Kombat universe murdering Batman, The Joker, Superman, and others from DC comic books is revolutionary in its own right. It required some hoops to be jumped through in terms of fatalities, but NetherRealm managed to pull it off and the game is downright awesome. Who doesn't want to hear Scorpion tell Batman to "get over here?"
7. Soulcalibur With The Legend of Zelda
One of the things that makes Soulcalibur so cool is that it doesn't take itself too seriously. There have been all sorts of characters making guest appearances in the game, and some of them have been pretty weird. But where things really went off the rails was when Link from The Legend of Zelda found his way into the bloody fighting game. It was completely unexpected, and that's what made it so awesome!