A fictional crossover is the merger of multiple, otherwise separate, characters, settings or universes into one story. Official (or legal) crossovers are often seen in the world of comic books, screen media and traditional literature.
Official crossovers in video games are most often seen in fighting games such as the Marvel vs. Capcom series and Super Smash Bros. series. However, more recently titles such as Kingdom Hearts have been a surprise hit and more genre titles are now employing this concept.
Unofficial crossovers can be found in Fan Fiction and Fan Art among other fan projects which bring together assets from different fictional worlds without permission of the copyright holder.
