The Flash

In the film, Barry travels back in time to prevent his mother's death, which unintentionally results in his being stranded in an alternate past. Development of a film based on the Flash began in the late 1980s, with multiple writers and directors attached to the project through 2014.

Travelling back in time to prevent his mother's murder — for which his father was falsely imprisoned, as revealed in Zack Snyder's Justice League — Barry Allen/ The Flash (Ezra Miller) ends up causing a butterfly effect and venturing into alternate dimensions across the multiverse. That's how The Flash will involve at least two returning versions of Batman, played by Ben Affleck and Michael Keaton.