Warning: Potential minor spoilers for Zack Snyder's Justice League
The first trailer for Knightmare scene, which drew a lot of confusion from audiences when the movie debuted in 2016.
As time has ed, more has been revealed about the meaning and purpose of Zack Snyders's post-apocalyptic DCEU future, but there's still a lot we don't know, and Zack Snyder's Justice League could present even more questions than it does answers when it arrives in 2021. Already from the trailer we know the fates of several more of the Justice League, along with a few more tantalizing Easter eggs.
The key to understanding Zack Snyder's overall Justice League plan lies in the Knightmare, and as with any kind of time travel, things can get weird. In the case of Batman v Superman: Dawn of Justice, we've already seen the timeline fractured once, and the next time we see the Knightmare won't be the same version of Darkseid's Apokoliptic future as we glimpsed in Bruce's vision before he was visited by Flash.
Batman v Superman's Knightmare Split in the Timeline
There's still a lot of mystery surrounding the Knightmare scene in Batman v Superman, and Flash's subsequent trip through a hole in time to visit Bruce in the Batcave, but one thing's for certain: it changed things. There's numerous variations on time travel logic in fiction, and we don't entirely know the ins and outs of how Flash's visit impacted the timeline in this instance, but we do know that Bruce takes his words to "find us" seriously, and at the end of the movie he tells Diana of plans to assemble the "others."
It seems logical to assume the version of events leading up to the Knightmare future seen by Bruce is not the same version of events we see in Batman v Superman after Flash's visit. If Flash never visited him with a warning, his fears over Superman might not have been stoked as severely, and he also may not have attempted to form the Justice League as early. While Flash was "too soon" and failed to successfully warn Bruce of the true danger, his message was still ominous enough. The Knightmare provides little context about how the world arrived at that point other than Superman telling Batman "she was my world and you took her from me."
Thanks to reveals from Snyder, we know his original plan for Justice League (one he said he never shot), included Lois Lane getting killed by Darkseid and triggering the Knightmare. Flash traveled too far back in time, so Bruce lacked the context to know what to do about the message, but it still changed his actions, and thus altered the timeline.
Justice League's Knightmare is Different Because of Flash's Warning
The first trailer for Zack Snyder's Justice League gives a glimpse at the Knightmare again, only this might not be the same timeline as the one seen in Batman v Superman: Dawn of Justice. While that version didn't show any other heroes fighting alongside Batman, the Knightmare shot in the trailer highlights the Hall of Justice and some Easter eggs about some other fallen heroes like Aquaman's trident and Wonder Woman's shield.
Since the end of the Knightmare seen in Batman v Superman featured Batman being killed, it would seem there's not much story left to tell in that timeline, but if Batman's decisions were altered by Flash's visit, causing him to do things differently, such as forming the Justice League earlier than he would have, we could see the impact of that change in a new Knightmare timeline in Justice League.
While we don't know if Zack Snyder's Justice League is going to play out the same as Batman's death in the Batman v Superman Knightmare may have already been averted simply because of the butterfly effect of Flash's visit.
Zack Snyder's Justice League Saga Was All About Averting the Knightmare
Flash's now-famous message that "Lois Lane" is "the key" and that he was "too soon" spelled out a lot of the roap for what would happen with the Knightmare timeline. As explained by Zack Snyder, Lois was supposed to die in the Batcave, which made Superman blame Batman for her death and succumb to the anti-life equation. Bruce, Barry, and Victor work together to build a Cosmic Treill in the Batcave (in the same physical space Flash appears to Bruce), and Flash is supposed to then go back in time and warn Bruce that he needs to save Lois, which would prevent Superman from succumbing to the anti-life and stop the Knightmare from ever happening.
Bruce may not have understood Flash's warning, but he did know whatever the message was arrived "too soon." Armed with this information he makes new decisions in this branch of the timeline. It may not be enough to save Lois from dying, but when he finally arrives at the point of the Knightmare where it's time to send Flash back in time to warn a younger Bruce, he knows to send him through a different route.
We also know Flash alters the timeline again (or, technically for the first time, since the version of Flash seen time-traveling in Batman v Superman is from the future) in the third act of Zack Snyder's Justice League, so there's plenty of timeline fracturing going on (we've already even seen Ezra Miller's Barry Allen come face to face with Grant Gustin's Flash). We may not even know the full extent of it yet, but it is clear that things with the Knightmare are much more complicated than they appear. All this timeline splintering by The Flash is just a warm-up for The Flash solo movie where he's set to recreate a version of his most infamous timeline fracturing yet, taking inspiration from the Flashpoint comic and truly establishing the DC Multiverse on the big screen.
