Aha, you're talking about the Joker story where he becomes a lawyer for the Bat-family's rogues' gallery, right? That's 'The Joker: Devil's Advocate' from 1995. It's actually a pretty contained one-shot, so the cast isn't huge. The absolute core is, of course, the Joker himself, but written in a rare mode where he's using the legal system instead of a joy buzzer. Batman is the ever-present shadow over the whole thing, the reason the Joker is even doing this. And then there's Janet Van Dorne, the judge presiding over the case—she’s crucial because the plot spins entirely on her actions and the pressure she faces.
Honestly, most other villains are just cameos in the background of the courtroom. Two-Face gets a mention, I think, but it's really the triangle of Joker, Batman, and Judge Van Dorne that drives the story. It’s less about a sprawling cast and more about watching the Clown Prince of Crime twist a single, high-stakes situation. The whole thing feels like a bizarre chess game with only three pieces moving.