Pre-Crisis: Killer Croc. Edit: Well, he wasn't Robin yet, but...
Post-Crisis: Joker, iirc, and I think I do.
New 52: not taking into account lesser baddies, it was the Untitled in that town. Edit: wait, as Robin? No idea.
Rebirth: Black Mask. Edit: ah, crap, again, as Robin, no idea.
Edit: I need to stop and read better next time.