Elseworlds (3)

Supergirl, The Flash, Green Arrow and Superman face the battle of their lives.
Part 1 - The Flash - S05E09 "Elseworlds, Part 1"
Part 2 - Arrow - S07E09 "Elseworlds, Part 2"
Part 3 - Supergirl - S04E09 "Elseworlds, Part 3"