User blog comment:ZSomji16/The Flash (Season 4), Arrow (Season 6), Legends (Season 3), and Supergirl (Season 3) Villains and Big bads/@comment-24152851-20170327122115

Arrow: Trigon, since following the pattern of previous seasons we get a Teen Titans villain every even season. Richard Dragon could work too though.

Flash: I'm hoping the whole Rogues Gallery in general.

Legends: Idk, Atrocitus maybe?

Supergirl: Brainaic PLEASE, he already got robbed from Super III which certainly didn't help that crapsack film.