Phreya, an Assassin who will attack you as you hunt down Korkorran in a tomb - PPE Mod portrait
Phreya is encountered in During the Throne of Bhaal part of Hexxat's companion quest. Her special version of Soultaker is more like a melee version of a Poisoned Throwing Dagger, which also procs a Slow that bypasses magic resistance. But - she won't drop it, nor is she killable as she is wearing the infamous immortality belt. We can drool all we want about that dagger, but we won't get it.