Even after getting him down, I had hard time figuring out how to hit him – the ceiling was too low and slime would just push me back up above him. I think I got lucky and he just rolled to his doom due to the platform being sloped and enough of the stuff on it being cleared out ahead of time.
The thing is, I could have sworn I saw the same boss in a DC before the new levels were released, and I had no trouble with him at the time.