While The Flash has already cameoed in two movies (Batman v Superman: Dawn of Justice and Suicide Squad) and will have a full role in Justice League, his solo flick won't appear until 2018. With the shooting of the movie scheduled for early next year, there is plenty of time for the powers that be (Geoff Johns and director Rick Famuyiwa) to decide on the main antagonist, if they haven't decided already.
And this seems to be the case, according to Umberto Gonzales of The Wrap. According to the report, Flash will be pitted against multiple villains, the team being simply called The Rogues. This should be taken with a grain of salt, though, since no official confirmation has been issued.
Furthermore, if the director does decide on this team of villains, they seem to be easy pickings for the speedster. We already saw this in Suicide Squad, when Flash effortlessly captured Captain Boomerang.
His job would be even easier if we take into account another rumor (unconfirmed by the director at this point), that says that Flash will be joined in his solo flick by Cyborg, another very powerful Justice League member.
So who are the Rogues? Obviously, we already mentioned Captain Boomerang, portrayed by Jai Courtney. The others are Captain Cold, Pied Pieper, Trickster, Heat Wave, and the Top. Their so-called powers are self-explanatory.
Their chances to defeat Flash (and Cyborg, for that matter) are increased if they are also joined by Mirror Master (who can use special mirrors in order to trap enemies, travel to other dimensions, and others) and Weather Wizard (who can control the weather to various effects).
As we’ve mentioned, this should be taken with a grain of salt, even if a return of Captain Boomerang would be great.