Deegan retrieves the book and attempts to rewrite reality again. Arriving on Earth-1, Clark and Oliver fight Deegan and his forces while Alex, Barry, and Kara locate the Book of Destiny in the Time Vault and take it to Clark, who restores Barry, Oliver, and Kara to their real selves. They find Clark, who agrees to return with them to Earth-1 while Kara persuades Alex to release her. Barry and Oliver locate Cisco and persuade him to take them to Earth-38. Deegan and his forces, including the Earth-1 doppelgänger of Kara's adoptive sister Alex Danvers, are holding Kara at S.T.A.R. Oliver realizes the Superman impostor is actually Deegan before forcing him to save innocents while they escape to find Cisco. They confront Novu, who breaches away Earth-90's Flash, reclaims the book and returns it to Deegan, who writes a new reality in which Barry and Oliver are powerless criminals known as the Trigger Twins and are confronted by a black-suited Superman. to restore reality, where Earth-90's Flash warns them about Mar Novu / Monitor, who is testing worlds for an impending crisis. After stopping the breakout, Kate, as the vigilante Batwoman, rouses them from their hallucinatory state and tells them to leave Gotham. During a confrontation with inmate Nora Fries, Barry and Oliver are exposed to fear gas and believe each other to be Eobard Thawne and Malcolm Merlyn, respectively. They retrieve the "Book of Destiny" but Deegan escapes by causing a mass breakout. The trio, with the assistance of Caitlin and Diggle, break into Arkham to confront Deegan. They are bailed out by Wayne Enterprises' CEO Kate Kane, who tells them Deegan is at Arkham Asylum. In Gotham, Barry, Oliver and Kara are arrested by the GCPD. Oliver realizes the figure and Deegan were located in Gotham City. Cisco vibes Deegan and the mysterious figure, who sees them vibing him and tells the group that something is coming and they will not be able to stop it. After defeating A.M.A.Z.O., Clark returns to protect Earth-38. Cisco Ramon retrieves Oliver and Barry from Earth-38, with Kara and Clark helping.
Oliver and Barry use each other's abilities to escape and travel to Earth-38 to get help from Kara Danvers and acquaint themselves with her cousin Clark Kent and Lois Lane, at Smallville, Kansas. Team Flash does not believe them and locks them up in the S.T.A.R. The following day, Oliver Queen and Barry Allen wake up in each other's lives. On Earth-1, the same figure gives the book to Arkham Asylum psychiatrist John Deegan, who uses it to rewrite reality according to his will. On a ravaged Earth-90, The Flash escapes as a mysterious figure uses a powerful book.
The conclusion of "Elseworlds" revealed " Crisis on Infinite Earths" as the next crossover, which aired in December 2019 and January 2020.
In "Elseworlds", Arrowverse actors portray other roles and John Wesley Shipp reprises his role as Barry Allen / Flash from the 1990 series The Flash. The title of the crossover was announced at the end of September and filming began in October 2018. Throughout August and September that year, casting for the crossover-including Ruby Rose as Batwoman, Elizabeth Tulloch as Lois Lane, and the announcement that Tyler Hoechlin would return to portray Superman-was revealed. The crossover was confirmed in May 2018 at The CW's upfront presentation, where the inclusion of Batwoman and Gotham City were revealed. John Deegan over his work at Arkham Asylum. In the crossover, Green Arrow, Flash, and Supergirl are drawn to Gotham City to confront Dr. "Elseworlds" introduces the characters Batwoman and Lois Lane, and the fictional Gotham City, to the universe. The crossover event began on December 9, 2018, with The Flash, continued on Arrow on December 10, and concluded on Supergirl on December 11. " Elseworlds" is the fifth annual Arrowverse crossover event that features episodes of the live-action television series The Flash, Arrow, and Supergirl on The CW.