Batman is not a normal person. We've established this. However, what if, like a normal person, the events of Arkham City, and the death of the only person who seems to be able to truly relate to the Dark Knight, have left Batman with Post-Traumatic Stress Disorder? Could you imagine playing Arkham Knight and being treated to instances where Batman sees The Joker as his conscience in cut-scenes? Arkham Knight is meant to make the series go out with a bang, so there will be plenty of baddies, plenty of dangers, and Batman is an individual with a lot to lose. Not only is the city he cares about in grave danger, but so are the lives of everyone he holds dear: Alfred, Selina, Barbara, Dick, Tim, and Gordon. The Joker could be used to remind Batman of this, taking the role of Batman's dark conscience, pushing his buttons and urging Batman to take measures and travel down paths that the usual Batman would never consider. Joker could even remind Batman about how he caused the death of the beloved Talia al Ghul, the murder of Jason Todd, and was also responsible for the paralysis of Barbara, bluntly reminding Batman what happens when you allow deranged criminals to walk free instead of ending them when you have the chance. Also, imagine all the fun banter that could take place?