Warner Bros. has confirmed to Eurogamer that the Batman: Arkham City VIP pass (a code that comes in the retail box) unlocks the playable Catwoman content. While Warner Bros. says that "playing as Catwoman is not required to complete the game," to access her in the campaign missions you'll need to use the code. When Warner Bros. first started talking about Catwoman as a playable character, they noted that her part in the game's story was around 10 percent. Apparently you can play the game without her and her omission will not affect getting the Platinum Trophy on the PS3.
Without the VIP pass code, Catwoman still appears in the game as part of the storyline, but her playable missions remain locked, as do any achievements or trophies associated with her.
On Xbox 360 the Batman VIP pass costs 800 Microsoft Points and on the PlayStation 3 it costs £7.99, or around $10 USD.
Eurogamer uncovered this news from a video title screen. It read: "Catwoman is a unique character with her own story, moves, and weapons. Unlock Catwoman by redeeming the 1st purchaser included in the game case or by visiting Xbox Live Marketplace."