I decided to try to play a pacifist (along with some other challenges) thief character on hardcore difficulty, making the least possible number of kills while finishing as many quests as possible (this is actually almost necessary, as I get no combat experience). So far, I have finished 20 quests (I believe I'm about 2/3 through the storyline) without killing anyone, even though the character is a little suboptimal (it is my first playthrough).
There is, however, a problem with the dam quest. It can only be completed by getting rid of the Prospector. There are no handy traps to trick him into triggering, charming his own minions does not work as they cannot hurt him. The only remaining option is to weaken him, lure him all the way back to the Mayor (which is pretty difficult as he keeps summoning skeletons right next to you), then protect the Mayor from harm until he finishes him off. I managed to do this, but, unlike with any other friendly or hostile creature I encountered so far, Mayor's kills actually count as your own. A bug or a feature?
A question concerning the Mayor and Prospector [spoilers]
Re: A question concerning the Mayor and Prospector [spoilers
I know nothing about whether intentional or not the kill-count increase, but I have a very easy way to get rid of the small fry of the Prospector: Turn undead. They will flee for 100 round, it'll be more than enough for luring him to the Mayor.