Video game crossovers, much like crossovers in other forms of media, are not particularly rare. Companies have realized that by combining their brands with other well-known characters and franchises, they can vastly improve the popularity of both products. After all, fans love to see their favorite heroes and villains go to new worlds in whatever capacity they can.
This thinking, though, has led to some very weird video game mashups where the universes of two or more well-known series have been flung together haphazardly. It can feel like they were thought up by an 11 year old who just had way too much sugar.
Sometimes, these bizarre crossover video games are created as cheap marketing ploys that attempt to take advantage of hardcore fans, but others are just straight-up odd mixtures that you would never have expected to see.