Taking inspiration from The War of Jokes and Riddles, A Death in the Family, and The Killing Joke.
Riddler and Joker team up in Arkham to break out and kill Batman. Except, that Joker shoots Riddler and leaves him to die on their way out. With chaos brewing across the city after the mass breakout at Arkham, Joker and Riddler (who recovered quickly) each ally with other villains, now looking for revenge not only on Batman, but also each other. Both factions rampage through the city and fight each other whenever there are encounters, causing even more chaos and destruction.
After Joker's faction starts gaining more territory and causing more destruction, Batman is forced to ally with Riddler just to prevent Joker from plunging the city further into madness. Joker, hurt that Batman didn't choose him, decides that this is the end of the so-called "Bat-Family" is over, and he wants Batsy to himself. He goes to Commissioner Gordon's house, but finds Barbara and shoots her, then kidnaps Robin when he goes out on patrol by himself.
Batman is overcome by rage at the end, and nearly kills both Riddler and Joker, especially after Riddler reveals he orchestrated the war, just so Joker could laugh again. All villains are sent back to Arkham, and Bruce is left to mourn Jason and hope that Barbara survives.
