8. Alien Vs. Predator
Star Wars made three films based off a single twist and Snakes On A Plane kept its schlocky name under the pressure of Samuel L. Jackson, but the award for most contrived movie origin goes to Alien Vs. Predator. Coming from a background in-joke from Predator 2 and developing into a comic book series and series of popular video games, the film was intended as a way to rejuvenate the two failing adult sci-fi series. Instead, it pushed them to the brink of nonexistence. By the time the first film arrived there was already a pre-existing fanbase from all the spin off media (including, surprisingly, action figures), but it seems like 20th Century Fox assumed thered been no new developments in the series since Alien Resurrection in 1997. Ruining Aliens continuity by having Weyland appear two centuries too early and having Predators team up with humans thus making them infinitely less badass, the film wasn't just saying f**k you to fans of AVP, but those of the two original franchises too. The sequel was less destructive to the mythos, but did reduce two of the most formidable cinema monsters to boring slasher killers. Of course there is a happy ending. The two series were eventually by presenting modern spins on their respective first instalments.