I've encounted Enemy Unclean beast giving me plague and ozone effect which spawns awfully loads of damage, with damage number in 2 digits.
there were at least 4-5 stacked together every second. I don't know what item the AI used. When I used UB, even with attack speed items (there aren't a lot of other items to UB I can guess would give this ultra fast damage drain combo)
The damage drain rate is at least 600 per second, cause the level 13 health steal spell stealing 600hp/s could not cure the damage quick enough, and my UB was dead within 5 seconds. Wheras my UB with plague and ozone could not do such a damage no matter what I tried. Damage deal was always ticking second to second, and wasn't like the AI's which gave me 4-5 hits per second. It wasn't using melee attack on me either.
I wonder if it's using an orb like you said.