Curse of Pain
From Diablo Wiki
Curse of Pain is a spell cast by some monsters that inflicts continuous fire damage for a given period of time (v2.05). Curse of Destruction is a similar spell but that detonates eventually. 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 a dark smoke appearing above your head. One of the monsters that uses this spell is Diablo.