Trivia: Although this film marked Michael Keaton's return to the role of Batman, he was originally supposed to reprise the role the year prior in a Batgirl film, which also would have seen J.K. Simmons reprising the role of Commissioner Gordon from Justice League. Although it had completed filming and was gearing up for post-production, Warner Bros ultimately decided to cancel the film's release and ended up using it as a tax write-off.
Trivia: SPOILER: Nicolas Cage has a cameo in this film as an alternate version of Superman fighting a giant spider. This is a nod to the cancelled film "Superman Lives", which would have starred Cage and been directed by Tim Burton. The giant spider was part of the script at the insistence of producer Jon Peters, who finally got to make use of the idea in Wild Wild West.
Trivia: Director Andy Muschietti has a cameo as the guy who is about to eat the hot dog outside the courthouse.
Trivia: According to Kevin Smith, Christian Bale was repeatedly offered the cameo role of Bruce Wayne that ultimately ended up being played by George Clooney, but he wasn't interested.
Trivia: In the "chronobowl", many universes can be seen: one with the Superman of George Reeves, the Batman of Adam West, another with Jay Garrick, the very first Flash, Superman of Christopher Reeves, and Helen Slater's Supergirl.
Trivia: SPOILER: After Barry returns to his timeline, he discovers Bruce Wayne looks different, as he is now portrayed by George Clooney instead of Ben Affleck. In addition to being a nod to Clooney's portrayal from Batman and Robin, this could also be a sly way of removing Affleck from the DCEU, as he became disinterested in continuing to portray the character after Justice League.
Trivia: This film marks Ben Affleck's fourth appearance as Bruce Wayne/Batman (fifth if you count Zack Snyder's Justice League as a separate film). Although his time in the role has been a little fleeting, this technically makes him the actor with the most live action film roles as the character, edging out Christian Bale and Michael Keaton with three each (this film also being Keaton's third appearance).
Trivia: The focus of the marketing and even the release of this film had to be called in to question due to star Ezra Miller being mired in serious legal troubles prior to its release, including assault, harassment, and child grooming.
