By far my best character ever died because of such an unexpensive and easy-to-get item: Scroll of Detect Material.
I had some ridiculously over-enchanted gear, my weapons being two Flaming Adamant Swords +15, and all my armor GEF or Valpurium, enchants varying from +6 to +12. I had a bit less than 400 HP, and about all my stats were over 20. Oh, and he took on Danny in melee and survived victor.
After Ivan shamelessly stole my Elpuri kill, I proceeded past the portal. Everything went just fine until I reached the mage level, and was unable to skip it for I couldn't detect the damn staircase. I even got to the mages room, but I couldn't dispatch them in time.
No Al, you don't get it. If you encounter a mistress in a normal situation where you can see her before attacking, you can just "s"earch and wait for her to get close, and get the first strike. But when she's waiting you downstairs you have no chance to act before she knocks you unconscious.
Alveradok, I can assure you that mistress is at least as bad as Ur'Khan. You would need to have huge amounts of agility to even have a chance to act before your head turns into a wobbly mass and you pass out. If your head can survive the blow without severing, that is.
My worst bone file is by far in GC6. Right next to the staircase is a mistress torturing chief, armed with a +9 whip. I think I've lost three well geared characters there, the latest one having two +15 octiron thunder hammers.