"People have often asked why show dislike for Superman and cast disdain for superheroes. Some liken it to jealousy, that they have what I desire, and what money cannot buy, but I tell you today that it is simple fear. I see what Superman could do and dread the tyranny he could inflict on us, on the world, and shudder. So I've called you here today to ask all of you a simple question, what could be worse than one Superman? An infinite amount of him"-Lex Luthor, at the First Multiverse Symposium
Mister Mxyzptlk popped into existence onto an empty roof and gazed upon Metropolis. simultaneously, Mister Mxyzptlk popped into existence in empty rooftops in Gotham City, Star City, Central City, and looked in disappointment. Of all the superheroes he could see, all the supervillains he had met, all had been so boring. All had been so incapable of seeing the bigger picture behind the morality they both hid behind. And while he could admire sticking to a bit, and running jokes, time was running out. Even for a fifth-dimensional being like him, there were rules to follow, and personal intercession to save the universe from destruction just for entertainment would definitely break some of them.
Oh, he would bet on the so-called Justice League against regular villainy, the common Captain Colds, and Deathstroke, and even against some world-ending threats like the sloppily named Reverse-Flash and the Anti-Monitor, if he ever reared his ugly head, and he even believed that with substantial casualties the Justice League would win. His shenanigans, carefully molding the figurehead of the Justice League-Superman- would not go to waste, the pinnacle of raw power, honed for saving people and planets. But Mister Mxyzptlk did not just look through his eyes, he could "See", and what stories he could see frightened him. The collector of worlds, constantly thinking and planning to capture another, A businessman, making deals that the whole world would flinch at the cost. And most dangerously? A quiet Madman toiling, quietly for an Equation whose synthesis would herald destruction un-paralleled.
The Justice League contains versatile and powerful individuals, some of them; the ones Mxy crafted himself could protect the universe from one of the many threats seeking to destroy it, and maybe just maybe defeat another one. But a third, a fourth? The Justice League, facing another galactic threat would not be able to survive it, as the members would specialize for some of the imminent threats, but would not have the versatility for every threat there was. The most powerful would specialize for the biggest threats, causing the "medium weights" to become near obsolete, as they would be tied down by threats they couldn't ignore, yet couldn't delegate to lesser heroes.
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What the Justice League needed was another hero, or a multitude of lesser ones, allowing some to fight upwards in power, but Mxy didn't know of anything he, or anyone could do so he just looked out on the rooftops and saw. Saw the tapestry of creation, each individual action and its consequences, a balancing act that would snuff a lesser mind. The threads of fate weaving individuals together, splitting them apart. He Saw everything, and searched for the superheroes
He saw the grounds of Central City, a red streak lighting up the roads, traveling at speeds that would hurt for a mortal to comprehend. In Star City, a shadow, raining death in the form of a bow and arrow, seeking quiet cleansing of the city ruled by money. Gotham City, governing by fear, The Bat glides, seeking vengeance, and in his wake a shadow flickering a sidekick hopping from rooftop to rooftop, both chasing someone more feline than women. And Mxyzptlk's star, the Hero of Metropolis, flying valiantly around his city. Crime ceasing where his presence appeared. Mxy could sense more heroes, more stories just waiting to be told but there wasn't any time, and almost wept from the inability to change the future. His fellow imps, as useless as he was, as none were willing or able to change the dreaded future, which threatened everything Mxy worked for, a hilarious joke where Superman would get his costume color schemed switched, forcing Superman to have to wear... Orange.
Mister Mxyzptlk sighed again, resigning himself for a future without distractions, just the tedious and inane fifth dimension where he usually resided. His copy in Star City and Central City faded away, dispersing into nothing. Eyes closed, his copy in Gotham faded as well leaving just his true self. gazing upon Metropolis. He started forming his name in his head switching the pronunciation when a crack caused him to open his eyes to a world bathed in green.
"A firework" he whispered, gazing at the green light, which seemed to go even to the stars when Mister Mxyzptlk realized something. If Earth needed a hero, one mutable, and with incredible power, he realized just the tool to use. Transferring someone from one dimension to another was one thing, and bringing someone from another multiverse was exponentially harder, but permanently bringing someone from a multiverse that didn't even exist, would be almost impossible, for a regular Zrffian. But he was Mister Mxyzptlk, an not just any imp from the fifth dimension, but the imp from the fifth reality. And so he started to shape reality.
"It's a shame you won't be able to go back, but that's a small price for you to pay" Mxy whispered, "But better you pay it than this whole multiverse does"
Mister Mxyzptlk disappeared, the last of his copy vanishing and in his wake, he summoned two things, displaced two objects in the vast Multiverse, and dropped them in Gotham city, incidentally right into the path of three goons all sporting penguin icons. As the last traces of Mister Mxyzptlk were displaced, he wished good luck on the stranded objects he brought into a galactic struggle, someone from an Earth with no superheroes, and on his wrist, unknowingly, a watch; glowing green.