Nine thousand-year-old Nine Hells native Tony Manero lives for Saturday nights at the local disco, where he's king of the club, thanks to his stylish moves on the dance floor.
I believe this is more widespread than just certain bosses in certain dungeons. I've seen this occur in open zones with common creatures. I was recently running through Icespire Peak and was always getting hit by the Winter Wolves blast attack even when I was well outside of the red, highlighted area of effect.