Katars are weapons can only be equipped by the assassin class. Katars are always two-handed so you cannot wear a shield if you are using one. sonic_blow and grimtooth can only be used with Katars. The Critical rate is doubled with katar-type weapons. In spite of the fact that a katar wielding assassin has a blade in each hand, it counts as a single two-handed weapon rather than tow dual-wielded weapons, so righthand_mastery and lefthand_mastery have no effect on them.