Invasion!

Invasion! is the name of the 4 part crossover event between Supergirl, The Flash, Arrow and DC's Legends of Tomorrow that will air in November 2016. The episodes invovled in the crossover are:
 * Supergirl Season 2 Episode 8
 * The Flash Season 3 Episode 8
 * (Arrow)
 * (DC's Legends of Tomorrow)

Trivia

 * The crossover is marketed as Heroes v Aliens