Man, shadow priests are the most terrifying people in Azeroth. Even warlocks' motivations are still comprehensible, and honestly the void makes fel look tame. That said, most people write them off as eccentric until they watch one literally go crazy, murder everything, and then die scream-laughing. Or when they notice the tentacles during void form or hear them spout Old God gibberish.
YES! YESSSSS! FEAR US! THE OLD GODS FEAST UPON YOUR TERROR—
I mean, uh, confirmed. Yeah.