![Screenshot of an elite and minions with skull and crossbones icons over their heads](https://i.stack.imgur.com/pDgjx.jpg)

We have run across this skull and crossbones icon over a few enemies in Hell difficulty and we don't really know what it is. It doesn't appear to be consistent with effect names on elites. I did notice my character had a debuff in the screenshot (didn't notice it in game) and also has the skull and crossbones over his head. So what is this thing and what effects does it have on the monsters and the players?