Was messing around with the MG during the 12th Anniversary and was hit with Ring of Smoke twice. My, pet, and merc were at point blank range and hit me for about 17K the first time and 19K the second time with fire resists at 740. Destroyed my SK pet once (I parked him behind a rock and he wasn't hit the second time) and took my T5 healer merc down to ~50% both times we were hit.
Only seem to get hit with it when he resets (all the spawned mobs disappear) but they are hot patching and such to fix many issues so who knows how it will end up.