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human
[Justice League Unlimited] What would have happened if Lex Luthor had escaped in Flash's body?

In the episode where they swap minds, suppose that he had managed to successfully construct a teleporter and get himself off the space station. What would have happened next? How bad would it be for the League and the world in general? What would Luthor accomplish with his new body?
gpt
what he usually does, but much much much faster.

approximately one week after escaping the justice league are all wiped out as portals are opened at each of their individual locations and robot fighters, dozens of them and each hand tailored to counter their quarries powers, burst out.  Supes himself is tied up in a kryptonite infused rope by a powersuit wearing superspeed lex and is shot in the back of the head with a kryptonite bullet.

after that is where it gets interesting.  most of his previous allies in the injustice league get the same treatment as the justice league, having eliminated his rivals he has no more use for his allies.  But after that, he proceeds to distribute, at his own pace, the technological marvels he has created to humanity at large.  it starts slowly at first but soon the world starts seeming more and more like star trek or some other technotopia, and lex gains more and more control over humanity.

lex is more than anything a narcissist.  He hates superman because he hates the idea of someone superior to himself.  In this new techtopia things are...ok.  People who badmouth lex, even in private, find their lives ruined.  For everyone else life continues more or less as normal, within parameters specified in their lexcorp employee/citizenship contracts, but at the very highest levels humanity is managed and directed by one voice, one intelligence: an AI approximation of his own mind left behind by Lex hundreds of years previous.

Flash can live fast, not simply move fast.  Lex exploits this almost continuously, to multitask, to plot, to perform experiments, and as a result of living in his time bubble becomes disconnected with humanity.  Being a narcissist he assumes humanity needs *him* so he creates an AI backup to manage humanity while he uses the speed force and devices of his own design to explore the multiverse.