Prometheus: Cool to see some villains new to the Arkhamverse. I bet they'll focus more on the "cop killer" aspect, rather than the anti-Batman one since Arkham Knight already covered that.
Mad Hatter: Really indifferent on this one. The Wonderland aspect has been played out at this point, and the code description makes me think it'll be another fetching mission, this time with GCPD officers.
Ra's al Ghul: I'm pretty OK with this, if this means it'll tie-up some of the loose ends of
Arkham City.
Killer Croc: Again, this one makes sense. We saw his new model and design in the game. It'll be nice to see if we'll see how Scarecrow escape from his clutches.
Mr. Freeze: Not happy about this. I enjoyed the sense of closure that
Arkham City gave him, so to see him once again just for fan service is a huge waste. Plus, I'm afraid to see Rockstead lower one of the best bosses in the game into another tank battle.
Black Mask: Not really excited to see him. The Arkhamverse version of him is a weenie. Also, didn't Red Hood kill him in the DLC?