New copies of Batman: Arkham City come with an online pass giving you access to the playable character Catwoman. She will be part of the story and an extra feature of the game called "The Riddler's Revenge". She is "not required to complete the game" said Warner Bros in a statement.
If you were thinking of picking the game up used, you can still get a code from the PlayStation Network for $9.99 and Xbox Live for 800 MSP. I will be getting this day one, Catwoman is too sexy to pass up. Will you resist her charm?