Looks like the aliens from invasion, the Dominators, will be sticking around the CW DC Universe for a bit longer after the epic four part crossover that will go through Flash, Supergirl, Legends of Tomorrow, and Arrow.
According to CBR.com the Dominators will return to Supergirl later this season:
This is not the last you’ve seen of The Dominators,” Andrew Kreisberg, an executive producer on “Supergirl,” “The Flash,” “Arrow” and “DC”s Legends of Tomorrow, told a group of press including CBR during a Q&A Monday at The CW’s Burbank headquarters. “The Dominators will return on ‘Supergirl’ later this season.”
The Dominators first appeared in Adventure Comics #361, which can still be picked up on the cheap, and later came to prominence in DC’s Mini Series Invasion
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what are joke supergirl was , it was like reading comic with x y or z on the cover and they turn up on the last page