6. The Joker - Batman: Arkham City
So while the Joker isn't directly killed by Batman in the game it is through a combination of all the events from Arkham Asylum to City which puts the Joker in the state he is in at the end of the game. After the events of Arkham Asylum and the cordoning off of the new Arkham City, Batman goes in to have a nosy at what his good old friend The Joker is up to. As he comes to investigate the Joker proves he isn't just a pretty face and knocks out the Caped Crusader and infects him with the same blood which contains poisons of the Titan formula. The Joker reveals that he is dying from the disease and attempts to infect both Batman and Gotham with it. As the game progresses a cure for the poison is eventually found and finds its own way into Batmans hands. After fighting through the population of Arkham and finally confronting the Joker with a cure for the disease which is killing his nemesis, Batman hesitates. The Joker, however, acts too hasty and accidentally knocks the vial of antidote out of Batman's hands before he can decide what to do. As the Joker tries desperately to sip up what little antidote he can Batman admits he would have saved his nemesis, despite all the tragedies he has committed. As the Joker succumbs to the poison Batman takes the body of his nemesis out of the city and lays him on the hood of a nearby police car before leaving. The death of the Joker can be a hard hitter for fans of the series and casual fans alike, to see such a well recognized character die is quite tearful. Batman might not have directly killed the Joker but it was still a death which could have been prevented by the Dark Knight, a fact which will always haunt him.