"Crisis on Earth-X" might take the fight to two of the Arrowverse's worlds, but it also hinted at another inter-dimensional battle along the way.
Spoilers for "Crisis on Earth-X" below!
This year's crossover saw the return of Eobard Thawne/Reverse Flash (Tom Cavanagh), who previously terrorized the Arrowverse on both The Flash and Legends of Tomorrow. Eobard followed the Earth-Xers in their crusade, both to conquer Earth-1 and to steal the heart of Kara Danvers/Supergirl (Melissa Benoist).
When Eobard went to extract Kara's heart, she attempted to threaten him by saying that her cousin, Clark Kent/Superman (Tyler Hoechlin) would come to kill him. But as Eobard revealed, that wouldn't be a problem, because he's already fought and defeated Clark before -- in the future.
So, that begs the question: when and how will the Arrowverse's Superman fight the Reverse Flash? As it stands, the two operate on completely different Earths, although Eobard's Earth-X activities seem to hint that that isn't a problem for him.
The first assumption would be that it has to do with the crisis (no, not the one currently happening in the crossover), which has been teased in the Arrowverse since The Flash's premiere episode. But there's a chance that it could hint at a different story altogether: Time Masters: Vanishing Point.
The six-issue miniseries ran from 2010 to 2011, and placed many of DC's biggest heroes in a unique set of circumstances. The new Time Masters consisted of Rip Hunter (a name familiar to Arrowverse fans), Green Lantern, Booster Gold, and Superman, as they traveled through time attempting to locate Batman. Along the way, they eventually ran into Eobard, who gave the team of heroes a run for their money.
Could a version of this storyline make its way into the Arrowverse's future? Possibly, and having Hoechlin's Superman as a part of it would certainly resonate with fans. Fans will just have to stay tuned into the four Arrowverse shows to see what happens next.
"Crisis on Earth-X" concludes tonight with episodes of The CW's The Flash and Legends of Tomorrow beginning at 8/7c.