It would be great if Vandal Savage showed up.
One idea is this. He turned out to'd been pulling strings such as behind Amanda Waller and Batman's parent's deaths along with Ra's Al Ghul who is his accomplise.
One of the actors I pictured for him is Jason Isaacs.... best known as Lucious Malfoy on Harry Potter. He can do a great job with playing someone who seems a charming gentleman but can prove a very dark man.