User blog comment:ZSomji16/The Flash (Season 4), Arrow (Season 6), Legends (Season 3), and Supergirl (Season 3) Villains and Big bads/@comment-25280771-20170327151617

My idea is that the Legion of Doom will get bigger and bring up all the villains for the new seasons:

Arrow: Richard Dragon or Constantine Drakon (working with Malcom Merlyn)

The Flash: Cobalt Blue (working with the Reverse-Flash) + Captain Cold and his Rogues, maybe Gorilla Grodd

Legends: Reverse-Flash, Damien Darhk, more Members of the Legion of Doom

Supergirl: Maybe a Luthor or a group of villains (could be part-time members of the Legion of Doom)