This is pure speculation, but according to a tweet by retailer Best Buy (see below), their store exclusive pre-order DLC allows the player to play as Bruce Waynes (and Talia al Ghul's) son Damian Wayne, presumably in a rendition of the batsuit he wore in issue #666 (also below), where he featured as a much darker, less moral Batman.
Some however have suspected that Damian Wayne may instead be the Arkham Knight. Although the approach of the character would fit Damian's mentality and echo the warnings given to Batman in Arkham City from Azarel, it is highly unlikely that a much demanded character like the Arkham Knight would be given away as a store exclusive pre-order DLC.
