Watch The Flash “Elseworlds”, the fifth annual Arrowverse crossover event, featuring episodes of the live-action television series The Flash, Arrow, and Supergirl on The CW.
The crossover begin on December 9, 2018, with The Flash, continue on Arrow on December 10, and conclude on Supergirl on December 11.
“Elseworlds” will introduce the characters Batwoman and Lois Lane to the universe, as well as the fictional Gotham City. In the crossover, Green Arrow, Flash, and Supergirl are drawn to Gotham City to confront Dr. John Deegan over his work at Arkham Asylum.
On Earth-90, many heroes have been defeated and the world is ravaged. The Flash of this Earth crawls towards a mysterious book, only for the Monitor to tell him he has failed and that his world will perish. The Flash is able to run away before the Monitor can do this.