Invasion! (4)

After learning the Dominators’ plan for the world, the Legends must work together with The Flash, Supergirl and Green Arrow to kill them once and for all. Meanwhile, Stein figures out, with the help of others, how the team can terminate the Dominators, but is distracted by the aberration he realizes he created in 1987.
Part 1 - Supergirl - S02E08
Part 2 - The Flash - S03E08
Part 3 - Arrow - S05E08
Part 4 - DC's Legends of Tomorrow - S02E07