Its not a weapon based skill, formally it is a spell. That creates knives with piercing and bleeding damage. These knives do not act quite like normal spells though, they convey flat damage and effects from equipment, as if they were indeed weapon attack. Like chance of flat physical from rage of Ares relic or burning from earth enchantment. And poison from envenom weapon. Envenom weapon was one of the main reasons people were using it at all, because their own damage is low and too low for legendary. Most of the time its just to spread slow and confusion, a crowd control skill. It can be built around with some good items.