The last moments in Arrowverse's 2018 "Elseworlds" crossover could change the multiverse as we know it – 2019 Arrowverse crossover has been confirmed as "Crisis on Infinite Earths", an adaptation of a massive crossover story from DC Comics.
The label at the end of "Elseworld's Part 3" promised that "Crisis on Infinite Earths" comes in "Fall 2019", rather than the crossover's usual wintertime slots, which means that the upcoming crisis may affect the entire season of Arrow, The Flash, Supergirl and DCs Legends of Tomorrow.
Crisis on Infinite Earth's storyline in DC Comics was written by Marv Wolfman with the art of George Pérez and ran for 12 questions from March 1985 to April 1986. As we break into our explainer on the screen and his nemesis, during the crisis "the monitor recruited 15 heroes from different worlds to join the fight against the anti-monitor. The goal of the monitor was to enter the multiverse of a single universe with the power to resist the attack of the anti-monitor. Ultimately killed during this conflict, his plan succeeded. DC multiverse shrunk into a single universe, resulting in a renewed world where the heroes of Earth-1, Earth-2, Earth-4, Earth and Earth-X coexist now. "
Can we see something similar in DC TV Arrowverse, with Supergirl (and maybe the heroes of Black Lightning) being merged with Earth-1 heroes like The Flash, Arrow and Batwoman? We have to wait until next fall to find out.