The character, who had appeared in the episode "Survivors" (co-written by Eric Carrasco, who also co-wrote this week's episode), had been kidnapping humans who had the genetic capability to withstand a lifetime of hard labor to the interplanetary slave trade.
One of the buyers, who came in at a key moment in the story? A Dominator.
If you don't remember the Dominators, they're the villains who invaded Earth-1 during the "Invasion!" event. Supergirl was called in to help The Flash, Green Arrow, and the crew of the Waverider fend off the alien menace, and during the run-up to the big, final battle, she revealed that the Dominators existed in her universe, too, and had attacked Krypton at one point.
"This is not the last you see of the Dominators," Kreisberg told reporters during a screening of the crossover back in November. "The Dominators will return on Supergirl later this season."
Turns out, fans didn't need to wait long: The Dominators showed up tonight...on the very next episode of Supergirl following the crossover.
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