Checked, no one mentioned him, so I'd go with Temple Fugate, the original Clock King of Batman TAS.
He's a closet lolcow who became a horrorcow, and his descent requires an explanation of his debut episode.
He used to be a very successful lawyer who had an :autism: level obsession with being on time, and when he's involved in a case against him, the lawyer opposing him in the case (who holds nothing personal against him outside of his job) suggested Fugate chill for awhile before the trial because he was all keyed up and there was still a little time before the trial to unwind.
Fugate does this, and due to some unfortunate mishaps, is late for the trial, the court automatically declares against him for this, he gets ruined.
Fast forward to present day, that lawyer who gave Fugate the advice to relax becomes Gotham's mayor, and Fugate reappears to kidnap the guy and both make his life hell and eventually kill him, presumably for being the agent of his fall from grace.
He's a lolcow at this point because he's pursuing a stupid revenge scheme over crap the now mayor was not at fault for, or so it seems. Fugate then proceeds to get Batman involved in said scheme in an attempt to get rid of him as a potential threat, and the
in this is that Batman would not have known about him at all had Fugate not tried to get his attention.
To be fair to Fugate, despite his idiocy, he does manage to make Batman's life hell for most of the episode using his autistic devotion to time to escape Batman on a train due to perfect timing, puts Batman through several traps that Bats escapes only by sheer luck in some cases because Fugate really thought ahead, and is even able to fight Batman to a standstill because while he's a bad fighter, he watched footage of Batman to the point he knows the exact timing of Batman's punches.
Regardless, Batman manages to foil his scheme and defeat Fugate, and the man becomes a full on horrorcow when we discover the real reason for his deranged revenge scheme.
He wanted revenge not because he was financially ruined by that screwed up court day, but because the mayor MADE HIM LATE THAT DAY.
That's right, all the attempts to murder the mayor and make Batman's life forfeit at the same time was spurred by the butthurt of a sociopathic, time obsessed autist who took advice of his own volition that screwed him over because of circumstances no one could have foreseen, and he wanted to kill and hurt people because his autism backfired due to his own decision to accept the advice to screw around before the trial went awry and broke his perfect schedule.
He got a few more appearances since, but it's his debut episode where the batshit autism was on full display.
