Invasion! (Arrowverse)

"Invasion!" is the third Arrowverse crossover event, with episodes of the 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 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 main three episodes were titled "Invasion!". In the crossover, Barry Allen recruits Kara Danvers / Supergirl from Earth-38 to Earth-1 to help his team, Oliver Queen and his team, and the Legends to defeat the alien race known as the Dominators. Development of a crossover between the three series and Supergirl began in May 2016, when it was learned that Supergirl would move to The CW from CBS for its second season. By the following September the scripts for each episode were written, and were filmed in October 2016. The premise and episode titles were also announced in September. In "Invasion!", the main cast members of each series appear in (at least) their own series; Melissa Benoist appears as Supergirl in the entire crossover. A number of actors and characters from previous Arrow seasons returned to reprise their roles, since Arrow's episode doubled as its 100th. The three episodes of the crossover received positive reviews, with critics praising the interaction among the actors in each series and each episode's advancing season storylines as part of the crossover. The Dominators storyline was regarded as its weakest link, with reviewers finding the alien race's motivations unclear. Ratings for the episodes were high, with each breaking records in viewership and the 18–49 rating and contributing to the most-watched week on The CW in six years. A...