Speculation but possible SPOILERS for the FLASH movie follow:
From set footage and cryptic comments by actors, the villain for the upcoming Flash movie is becoming clear and it's kind of a surprising one. I had assumed The Reverse Flash would be involved somehow, but it looks like they are going in a slightly different direction by having Barry Allen dealing with a duplicate of himself. We have seen the stand-in sharing scenes, dressed to look identical to Ezra Miller (except with yellow lining on his sneaker rather than the Red that Miller is wearing, hmmm...). I'm not sure how I feel about this - I am not a big fan of Miller in the title role, so two of him doesn't really help things in my eyes. Still, this is all speculation, we probably won't get any concrete answers until the DC Fandome presentation in a few months.