Detective Comics, Vol. 1 #870 (2010)

Batman: Imposters, Part Four: Last Man Laughing
With the Impostor Joker Juice filling the fairgrounds all hell breaks loose, as the Joker mobs turn more insane than before. The fairgrounds have been littered with all manner of weapon, and the widespread panic and killing is just the thing the Batman Impostors need to break out their weapons and crack some skulls. It seems as though the creator of the Joker gas, Dr. Kaligari, might get to see his creation/experiment play out in full â but as with any tale the sees fit to punish the wrong-doer, Kaligari is killed by his vary creations while the Imposter Batman's identity is also revealed during his confrontation with the real Batman.
Release Date: 2010