I've always been bothered that we've never seen a side kick go bad and stay bad and I'm not talking about a situation like Jason Todd who was from a bad up bringing and already was prone to violence. I'm talking about someone who actually starts out idealistic and the perfect side kick but slowly becomes very damaged from the super hero life style. I got a thinking about this after playing Batman Arkham something Knight says caught my attention "I was just a kid! You turned me into a soldier sent me to war!" I'm amazed there has never been a villain like this I mean aside Jason (who let's face it has all sorts of red flags in his back ground) who just snaps from all the things side kicks (especially the young ones) are exposed to.
I think it would be interesting to see a young character(like on the Teen Titans team or whatever) slowly start to become unhinged developing symptoms of PTSD and some psychopathic/sociopathic tendencies like clearly show signs of enjoying violence maybe becoming like the Punisher and starting to view the other heroes as part of the problem(since clearly a lot of super villains treat the system as a revolving door and characters like Amanda Waller get to do all sorts of horrible things with organizations like Cadmus without consequence) I mean the heroes of DC might see such a character as having a psychotic breakdown but an argument could be made that the person is just realizing how crazy everything is I mean the JL fight crime lock up criminals the criminals break out kill a bunch of people get locked up again rinse repeat. I think it would be interesting to see one of the JL face a enemy they themselves mentored and ultimately went bad because they weren't paying attention and or noticing clear signs of that person's psyche crumbling especially if some hypocritical and morally questionable activitiy by the Justice League (I think they've done some morally grey things in the past) was the root of said fallen side kick's psychotic break down resulting in something like this.