4. Technically A Batman/Star Wars Crossover Film Exists - Batman: Mask of the Phantasm
Mask of the Phantasm is without question the most underrated Batman movie of all time. Whenever a Batman debate comes up (which they often do on this site), this film is rarely bought up. The movie follows Batman after he is wrongly implicated in a bunch of murders of bad guys actually perpetrated by a badass vigilante assassin. The film also features The Joker, brilliantly voiced by Mark Hamill. During the end of the film, The Joker shoots down a bunch a robots, and the sound that they make winding down is the sound of the Millennium Falcon winding down from Star Wars: Episode V - The Empire Strikes Back, which starred Hamill. So, maybe the idea of a crossover film is a bit of a stretch, but that is still a cool piece of information.