4) Deacon Blackfire (Arrow)
Most recognizable as a Batman villain (though it’s not as if Arrow hasn’t already borrowed plenty of those), Deacon Blackfire could definitely work as the show’s next big bad, and might just lead to a return for Matt Ryan’s John Constantine.
While Star City has obviously come under fire in every season of Arrow so far, the difference with Blackfire is that he actually manipulates an army of the homeless and disenfranchised to help him take over, and after attacks from everyone from Deathstroke to Damien Darhk, there are now plenty of those in the Green Arrow’s home.
That would help this villain’s mission to tie into previous years in a natural way and would also pit the titular hero against the people he’s actually trying to save.
The cult leader even managed to brainwash Batman at one point, so the same thing could happen to Oliver Queen, which would make for a very fun episode to watch.