Curse of Anguish
From Diablo Wiki
Curse of Anguish is a spell cast by some monsters that makes you take more damage from attacks and that reduces your healing potential (v2.05). There are two ways to see if you are affected by this spell. First, there is a little icon above the "Achievements" icon in the menu bar that appears. Hovering over this icon tells you how many seconds are left before the spell terminates. Second, when you are under this spell, there is dark smoke appearing above your head. One of the monsters that uses this spell is Diablo.