User blog comment:ZSomji16/The Flash (Season 4), Arrow (Season 6), Legends (Season 3), and Supergirl (Season 3) Villains and Big bads/@comment-31614978-20170327222256

Flash - At this point I feel there needs to be some development on the Rogue front.

A few weeks ago I would have said Abra Kadabra and have form the Rogues, but I guess that'll depend on how he's portrayed in tomorrows episode. I can see Killer Frost having a strong emotional connection needed for big bad material. However I love Danielle Panabaker too much to want her in a position where she might leave the show, yet if she must be a big bad, I can see her being the founder of the Rogues in her attemp to establish her own dark version of Team Flash.

Arrow - Not entirely sure where they could go without rehashing old material. Maybe the Outsiders from Jeff Lemire's GA run, if they're careful not to make them too similar the League of Assasins.

Legends - Maybe the Thanagarian? Or a dark version of the Time Masters...considering how dark the Time Masters were, an eviller version of them.

Or maybe the Time Trapper, or the Legion of Supervillains (from the 30th century)...

Supergirl - Brainiac! I want Brainiac!

Or I suppose the Legion of Supervillains could work here too. It would play into Supergirls canon history with the Legion of Superheroes.