By request, I bring to you (WITH SPOILER WARNING)
Black Mask
After the deaths or incarceration of most of Gotham's criminal underworld after TDK, several replacements came in. Some, like Oswald Cobblepot, had eccentricities that led to them getting colorful names befitting people like the Joker. Others, like Rupert Thorne, were more traditional mobsters. Roman Sionis was somewhere in between. His organization seemed to be much like the operations of Falcone and Maroni, only it had the sadistic daring that would make the Joker proud. Nobody was safe from the "Black Masks", especially those in Thorne's organization. Thorne's sister was murdered in front of her Kindergarten class, for example, and Thorne's brother (a doctor) saw his license be revoked. The GCPD was powerless to stop him, as he had several key business connections that allowed him to sneak through the system. Even the Batman could do little, as Sionis had a trump card: a former CSI from the GCPD who had examined several of the people who had apparently been murdered by Batman had proof, PROOF, that it was not Batman but Harvey Dent that killed them. Not wanting to plunge his city into a darkness beyond help, Batman had to instead wait for the true authorities to get him.
Thorne's gang, however, would have nothing like this. When Thorne's wife was kidnapped and tortured by Sionis (just for kicks), the gloves were off. Thorne sent his best men to get him, and get him they did: They took him and threw him into a vat of hot molasses. He survived, barely, but was grotesquely disfigured, especially his face, which had essentially become a bleached black and his skin had become hard, almost like bone. He also became even more sadistic. With this, he became the Black Mask, the most feared criminal mastermind in Gotham.
He would be roughly shown like the "War Games" Black Mask. That guy was a total creep. In my hypothetical "Riddler" storyline for B3, he would strike a deal with the Riddler: If Black Mask gets the ex-CSI to reveal the truth about the "Batman Murders" and thus restore the Batman to the infallible figure that the Riddler imagines him to be, the Riddler will kill Tony Zucco, the man who threw Black Mask into that vat of Molasses (this would lead to irony when Batman saves Zucco... thus also condemning the Flying Graysons to death in the future)