What Happened To Everyone Who Killed Batman?

When 2001 saw a curious Mr. Mxyzptlk decide that he wanted to see what a human would do with just 1% of the imp's powers, Mxy opted for the Joker as the one to get these otherworldly abilities.

The Joker being the Joker, of course, he managed to trick Mr. Mxyzptlk into giving up 99.99% of his powers - and thus, that was the crux of 2000's Emperor Joker tale.

Said tale is actually a Superman story, with the Man of Steel in a race against time to stop the Clown Prince of Crime's ever-expanding, reality-altering reign of terror. As part of this nine-issue extravaganza, the Joker eats the entire nation of China, murders Lex Luthor and violently kills a corrupted Jimmy Olsen.

In terms of Batman, that's where the Emperor Joker arc gets really messed up - as the Jester of Genocide tortures and kills Batman every single day before bringing him back to life the following day and repeating this process.

It's his relationship with Batman that's Mr. J's downfall, as Superman realises that the Joker could never fully destroy the world due to his unwillingness to permanently erase Bats.

From there, Mr. Mxyzptlk and Spectre rebuild reality, but the Man of Steel has to steal Batman's memories to stop the traumatised Bruce from reliving his multitude of deaths.