Available after you reach Chapter 5, the Extra Mode is a special offline, single-player gameplay mode that allows you to create a custom character and play through missions parallel to Ethan Waber in the main Story Mode.
Extra Mode is much like the online mode, except with new and unique missions and allies associated with it. As you encounter more NPCs in the Story Mode, and unlock new locations and side-missions, more becomes available in the Extra Mode. Thus, the Extra Mode is a reward for accomplishing things in the main Story Mode.
