I don't have a screenshot, but on the second time around I decided to go for the Destroyer title again. My Mystic didn't take on a couple at a time, he just rolled up his sleeves and annihilated every last one of them, all at once. Stoneskin, Haste, Mana Fortification, and a some healing and mana potions. I'd just step out of the way if they were getting too close.
Then, I just kept casting Supernova Level 6 until they all died, taking time only to refresh my Mana Fort, Haste, Mana and Health.
(Was it wrong to cackle devilishly while some guards ran away, as I cast spells after them?)