when does the flash show up in supergirl
Supergirl (TV series) On February 3, 2016, it was announced that Grant Gustin, who appears as Barry Allen / Flash on The Flash, would appear in the eighteenth episode of the first season, "Worlds Finest".[113] While no plot details on the episodes were released at the time, Ross A. Lincoln of Deadline.com noted that "the in-universe reason" for the crossover was due to Barry's ability to travel to various dimensions, thus implying that Supergirl exists on an alternate Earth to the Arrowverse in a multiverse.[114] The Flash episode "Welcome to Earth-2" confirmed this, showing an image of Benoist as Supergirl during a sequence where characters travel through that multiverse.[115] The earth that the series inhabits is Earth-38 in the Arrowverse multiverse,[116] and has been informally referred to as "Earth-CBS" by Marc Guggenheim, one of the creators of Arrow.[117]
Invasion! (Arrowverse) "Invasion!" is the third annual Arrowverse crossover event, crossing over episodes of the Arrowverse television series The Flash, Arrow and Legends of Tomorrow on The CW, and is inspired by the 1989 comic miniseries Invasion!. Events at the end of the Supergirl episode "Medusa" on November 28, 2016 marked the beginning of the crossover, which officially began on November 29 with The Flash, continued on Arrow on November 30, and concluded on Legends of Tomorrow on December 1. Each of the latter three episodes were titled "Invasion!". "Invasion!" sees Barry Allen recruit Kara Danvers / Supergirl to his Earth to help his team, Oliver Queen and his team, and the Legends to defeat the alien race known as the Dominators.