What are the online codes for batman arkham city?

People keep talking about online codes for batman arkham city and I bought mine used so I have no idea what they mean... what are they?What are the online codes for batman arkham city?
if you bought your game used then you do not have Catwoman story.

If you bought your game new it comes with it.

Catwoman story cost roughly about $5 i think or maybe $10.

Other codes are Nightwing (only challenge mode) and Robin (I think. Havent heard anything from him yet) and the Batman skins.

chucky cheese

elder of scrolls