Dont know whether this was a bug or not, but the Dalaran Spellscribe (level 21), a rare spawn just “Froze” me for 15 seconds while dmging me for 50 per second (all the same debuff). Was attacking the 3 adds so i focus on his casts… my bad, but still be aware!
When i looked for him on wowhead the spell says “3 sec stun”, but I was stunned from 100% to death at level 23!
So in HC never face him without heal or alone at all!
Best wishes