Get-a-Life Boy saysPart 2 of the 4-part Heroes vs Aliens crossover event.
Supergirl (who is from Berlanti Earth-38) visits Berlanti Earth-1 to help fight a Dominator invasion of Earth. Supergirl mentions that in her universe she learned about the Dominators in school on Krypton, presumably the same race (possibly able to travel between parallel Earths?)
