The Joker has always been a very grounded villain. He has no superpowers. He’s just a guy who looks like a clown. His abilities are not what makes him special or dangerous. There is nothing he won’t do to get the last laugh on Batman. It’s his cunning that can make him even a threat to the likes of Superman, as seen in the lead-in to the video game Injustice, where Joker’s actions trick Superman into killing Lois Lane and blowing up Metropolis.
However, Joker, for all his simplicity, at one point was the most powerful entity on Earth. In the Emperor Joker story, Joker gains the ability to manipulate reality itself. He develops the power to kill Batman over and over again, devour Chinese food out of a take-out container, turn the Flash into an obese, sluggish hero, and other bizarre, ironic cosmic jokes. The question remains, however, how did he do it?
Mister Mxyzptlk is one of Superman’s reoccurring villains. He’s a fifth-dimensional entity who comes to Earth every-so-often not to cause true harm but to play silly pranks. With his extra-dimensional abilities, he’s able to rewrite the laws of reality. His only weakness is, if you can trick Mxyzptlk into saying his own name backward, he’ll return to his own dimension for awhile.
Bored of playing straightforward pranks on Superman, Mister Mxyzptlk decided to see what might happen if he gave a fraction of his abilities to a random DC villain. He chose to give Joker 1% of his power, just to see what jokes the Clown Prince of Crime might pull off. However, what he did not expect was that the Joker might trick Mister Mxyzptlk into revealing his real name, which resulted in Joker stealing not 1% but 99.9% of his power.
In 69 seconds, Joker re-invented the world with his new fifth-dimensional powers, turning Mister Mxyzptlk into his prisoner and the world into a true joke. Most savage of all, however, was what Joker did to Batman. Every day, Joker would kill Batman in a new, horrific way and then bring him back to life, only to do it all the next day.
Superman, the Spectre, and Mister Mxyzptlk himself remained among the few people who were consciously aware that the world had changed, so they started to undermine Joker as best they could, given the circumstances. However, Superman was a plaything to the Joker with his God-like powers, and, with so little of his power, Mister Mxyzptlk couldn’t reclaim his powers on his own. The Joker’s abilities would soon result in the destruction of all reality, leaving everything a terrible, empty void.
However, before Joker could erase reality, Superman brought to Joker’s attention one simple thing: he could not kill Batman. Joker tries to disprove this by killing Batman, but every time, Joker instinctively brought Batman back. Joker couldn’t bear to destroy Batman for long, which meant that, if Joker destroyed the world, he’d forever destroy Batman.
This existential dilemma left Joker without any control of his powers. Spectre and Mister Mxyzptlk stole back the Joker’s power, reverting the world to as it was seconds before Joker transformed the world. The Joker was left in a catatonic state after all was said and done — but so was Batman. Having died over and over again so many times, Batman had been left permanently traumatized by the event. Superman volunteered to take the memories on himself, leaving himself traumatized and in pain so Batman could live.
There is one alternative version of Emperor Joker that many people overlook. In the animated series Batman: The Brave and the Bold, Joker is accidentally given the power of the inter-dimensional Batman Bat-Mite, transforming into a version of Emperor Joker. This leads to a less intense and sinister version of the same storyline, but it ends in a different fashion.
After being killed over and over again, Batman declares that Joker has taken away everything from him except for his sanity. To solve this, Joker invades Batman’s mind, only for Batman to imagine a world where he is no longer present. This results in a broken, mad Gotham, but without Batman, there is no Joker. This leads Joker into his existential crisis, during which Bat-Mite and a mute-Harley Quinn steal back Bat-Mite’s powers from the Joker.
Joker conquered the DC Universe with the powers of a cosmic entity. But how did this nightmare situation happen?