Justice League: Gods and Monsters (2015)
In an alternate universe, the Justice League only has 3 members and they are not all the goody-goody glory of the Justice League we know. So be it if you must kill off a few people for the greater good.
Superman, Batman and Wonder Woman stem from completely different past events and only with the help of Lex Luthor can they come to terms with some of their mistakes. A cross over to the universe we know would definitely give them a different perspective.
Lex Luthor is not his power hungry self and I seem to recall he does get the chance to meet the Lex Luthor and Justice League of the timeline that is more mainstream.
A decent movie if you’re looking for a new take. Purists will hate it. I enjoyed the what if equation of the movie.