Kilshevex:
BE VERY CAREFUL.
Though it does not state it, Mutilate requires DUAL DAGGERS. Unlike Backstab that states the same, ("requires daggers") where you can have a dagger in the main and whatever else in the offhand and still use it, Mutilate will not let you do that. You will get an error for lacking an offhand dagger.
It is also a "from behind" skill, though it states that.