Blackmist is a reward from a demon and you really need to be evil to obtain it.
SPOILER
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In Drow city during the summoning ritual give the demon the REAL Silver Dragon eggs and you will be rewarded with the Blackmist Halberd. You will also have to kill the silver Dragon to escape the Underdark, but you will also be able to get the human skin armour (after collecting the Silver Dragon blood.) This is from memory but I think it's all correct.
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It's bleedin dark down here, slippery too.
Man, that's a pisser.
