Elseworlds

Elseworlds is the name of the fifth Arrowverse crossover between, and. It began December 9, 2019, and finished on December 11, 2019.

Synopsis
The three-night event begins with Arkham Asylum doctor John Deegan rewriting reality, which results in Oliver and Barry swapping lives. In this new reality, the two heroes are the only ones that know that they are in the wrong lives and have each other's powers.