The Flash INVASION! Season 3 Episode 8 br br THE FLASH, Arrow, Legends, Supergirl - Extended Preview - S3E08 "Invasion!" - 4 Night Crossover Event - The CW br br Barry asks Green Arrow for help when aliens attack Central City, but when they realize that won't be enough, they track down the Legends of Tomorrow so they can bring Supergirl in on the battle.