Crisis on Earth-X

Crisis on Earth-X is the name of the fourth Arrowverse crossover between, , ​​​​​ and. It began November 27, 2017 and finished on November 28, 2017.

Synopsis
Barry and Iris’s wedding brings the gang together, but things go awry when villains from Earth-X attack the ceremony. All of the superheroes band together with help from their super friends like Citizen Cold, The Ray, Felicity Smoak, Iris West and Alex Danvers to take on their most formidable villains yet. Earth's mightiest heroes - Green Arrow, Supergirl, The Flash and White Canary - lead their teams into battle to save the world.