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I would suggest to check the Baldurash for the possible fix. Though I have to say that I have whacked the liches and vampires dead with a single and first hit, yet some skeleton warrior or mummy doesn't get "obliterated", always makes the save throws. For example, I went to Twisted Rune and the lich there came out. I managed to throw the Azuredge just before he spoke to me. The result was: he sait to me "Stop." and then BLAM! He was killed with the first hit
Same fate met the Vampire there, he was killed with the first hit as soon as I saw hit. After that I ran into some skeleton warriors in Cemetary and I had to BEAT them into bone dust with the Azuredge, because they always made the saving throws.
I have killed with it the vamps so that there is no "smokey" could. No gaseous form. Simply tells "Undead destroyed" and done, vamp corpse is lying on the ground and no gaseous form. Funny is to kill the gaseous form with the Vorpal Sword too. Have killed the genies like this, who turn into gaseous form. Just that I didn't get the XP from that sadly heh..