DC Entertainment and Warner Bros. have already turned The Flash into a success on the small screen with their CW series, and next the character is set to cameo in Batman V Superman: Dawn of Justice. Though it isn't as simple as that; The Flash appearing in Batman V Superman will be played by Ezra Miller, not Grant Gustin, yet will still be the Barry Allen version of The Flash. For some viewers this might seem complicated, but thankfully DC lore is well suited for such idiosyncrasies, and any fan wishing to do so could use the multiverse theory to explain the existence of two versions of the same Flash.
But without even needing to go so far as to rectify the existence of TV-Flash with movie-Flash, a familiarity with the character is likely to come in handy when he zooms on screen during Batman V Superman. In a recent interview, director Zack Snyder refers to Flash's appearance as "a giant Easter egg" and hopes the scene will spur some serious fan debate. That suggests his time on screen will be brief but crucial, and it's possible the significance of The Flash's cameo will be overlooked by casual viewers. But for those that understand The Flash -- and in particular his ability to travel through time -- the scene may prove very telling.
We've already suspected that Batman V Superman would feature dream sequences, like the "Knightmare Batman" scenario in where we see the clips of Batman sporting desert gear. The EW article uses the phrasing, "laced with dream sequences for both Batman and Superman," which implies there's more than just this one scene. And as it turns put, The Flash's cameo in BvS comes during one of these moments of questionable reality. It's questionable because, as Snyder sort of explains below, it'll be unclear whether The Flash is only a figment within Batman's dreams or a messenger from the future.
"We had such a straightforward narrative, on one hand, I wanted this other layer of the movie to be complicated and bizarre."
Batman V Superman is said to have a runtime of 151 minutes, so clearly there's plenty of time allowed for Snyder's straightforward narrative and this other bizarre layer (though it turns out Jena Malone didn't make the cut).
What exactly this bizarre layer is to Batman V Superman is up for debate, but if The Flash is shown delivering a "cryptic message" to Batman as EW reports, then there's every chance he could be delivering a vision or a plea from the future. Time travel certainly fits the bill as bizarre. And if The Flash brings evidence to Batman suggesting Superman is somehow responsible for the bleak future it's rumored Batman sees in his dreams -- where we had heard we may see a Darkseid easter egg -- then that's only more reason for the Dark Knight to want to take down the Man of Steel. After all, he's already super mad about Superman's fight with Zod raining destruction down on innocent people, just think how motivated he'll be to kick Superman's butt once he believes he's responsible for a hellish future.
Batman V Superman: Dawn of Justice opens on March 25, 2016, which is followed by Suicide Squad on August 5, 2016; Wonder Woman on June 23, 2017; Justice League Part One on November 17, 2017; The Flash on March 16, 2018; Aquaman on July 27, 2018; Shazam on April 5, 2019; Justice League Part Two on June 14, 2019; Cyborg on April 3, 2020; and Green Lantern Corps. on June 19, 2020.
Source: EW