"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. The crossover event began on December 9, 2018, with The Flash, continued on Arrow on December 10, and concluded on Supergirl on December 11.

What episode does Arrow Flash and Supergirl crossover?

The crossover began in Supergirl episode 2x8 "Medusa," though that was more of a teaser at the end of the episode (featuring the scene of Barry and Cisco recruiting Supergirl), and continues after the Flash episode in Arrow episode 5x8, also called "Invasion!," and ends with the Legends episode 2x7 "Invasion!"

Is Supergirl part of the Arrowverse?

Seven television series make up the bulk of the Arrowverse franchise: Arrow, The Flash, Supergirl, Legends of Tomorrow, Black Lightning, Batwoman and Superman & Lois, along with two web series, Vixen and Freedom Fighters: The Ray.