At the conclusion of Elseworlds (the Arrow, Flash and Supergirl three-night crossover event) it was revealed that Crisis on Infinite Earths will be the crossover event during Fall 2019. It is unclear if Legends of Tomorrow will take part in the event but given the scope of this, they likely could be (this event requires a lot of heroes and The CW is stacked with them, most days of the week). There is also the possibility that Batwoman could return regardless if her series is ordered by The CW as she could return in the same guest capacity Superman appears in. However, given the value of the Bat family, I doubt The CW would pass on having a crown jewel, in Kate Kane, in their DCTV Universe. Plus Batwoman could be their Batman substitute in this crisis if they wanted but they have the Legends too, so they can really mix and match whichever heroes they so please and need not follow the iconic DC lineup of heroes. Psycho-Pirate was also teased in the final part of Elseworlds and happens to be a key character and The Monitor's accomplice in Crisis on Infinite Earths. Also, if the DC series creators wanted, with this event and its repercussions, they could have Black Lightning folded into the greater Arrowverse. I'm just speculating of course and now it's your turn too, share your thoughts in the comments below.
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— Stephen Amell (@StephenAmell) December 12, 2018
Below is the synopsis of the comic written by Marv Wolfman with illustrations by George PĂ©rez.
This is the story that changed the DC Universe forever. A mysterious being known as the Anti-Monitor has begun a crusade across time to bring about the end of all existence. As alternate earths are systematically destroyed, the Monitor quickly assembles a team of super-heroes from across time and space to battle his counterpart and stop the destruction. DC's greatest heroes including Superman, Batman, Wonder Woman, Green Lantern, and Aquaman, assemble to stop the menace, but as they watch both the Flash and Supergirl die in battle, they begin to wonder if even all of the heroes in the world can stop this destructive force.
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The Monitor's goal was to contract the multiverse into one, singular universe with the strength to resist the Anti-Monitor's attacks. Though he was ultimately killed during the course of this conflict, his plan succeeded. The DC multiverse shrank into a single universe, resulting in a revamped world where the heroes of Earth-1, Earth-2, Earth-4, Earth-S and Earth-X now coexisted.
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For those who want more detailed spoilers, here are some here via the DC Comics Wikipage.
