I used Wand of fire on Goblet Shield and Yendor, then used Burst of Flame on the flaming cloud and it destroyed the Goblet (or the Wand of fire creature did) :D I assume the Goblet is not that immortal with the right combination :D
Had a nice game with Fire Mage, sadly I cannot finish, killing the Yendor is not working :) So it's a little bug report, the game overall is awesome, keep it up!