Spoilers!

I am not sure if this will work for other encounters, but when the shadow thief bumps into you and asks for help before vampires come, I discovered if you immidiatly attack the main vampire who will speak, she won't speak and that means her two lackey vampires just stand there waiting, while you kill them off one by one.

This is a variant of Fake Talk, as done by Duncan Clay, but it's such a universal (and obvious) cheese tactic that he's probably the first to document it. But anyway...

Supposedly, if you kill something that's trying to talk to you (blue-circle neutral instead of red-circle hostile), they won't fight back. This can be used to kill the "unkillables" in the game (things that aren't supposed to die before a certain point) but will SERIOUSLY screw the game up.

True. This is just one more cheap tactic. We, good gamers, would never use such a glitch.

Riiight ;)