Darken the Sky: All ranged weapon units may fire twice. No movement—only fire. Each Ranged Combat is resolved separately. If you do not have any units with ranged weapons, order 1 unit of your choice. (1 card)
NOTE: This means all ranged weapons units are considered “ordered.” While a unit cannot range fire if adjacent an enemy unit, if that changes during battling (perhaps because of fire from some other unit that eliminates or forces the adjacent unit to retreat), then the newly released unit is still ordered and may range fire.
I have two different reads on how the "Darken the Sky" card is played?
Each unit battles twice with retreats and hits resolved between each battle so the attacking unit may have to switch targets because it's first target either retreats out of range or is eliminated.