Edward Nigma, AKA the Riddler, is merely a highly intelligent man with a penchant for criminal activities. How dangerous can he possibly be? Looks like we'll find out in Batman: Arkham City.
As teased back in March, the Riddler plays a much more expanded role in Arkham City than he did in Arkham Asylum. No longer a faceless voice teasing Batman with puzzles, he is now something much more dark and dangerous. He's a criminal mastermind out to prove his worth, and when the Riddler sets out to impress, people get hurt.