It's basically a huge broadsword, and its main attack is a spin attack that hits 3 times. The added benefit is that, as a Unique-tier item, the Darkshard also pulls in enemies within a range of 5 meters (15 feet if you're a gun-user).
If one spams the Fighting Fungus to increase one's attack speed, then one can become a miniature targeted tornado of twirling steel and amethyst alloy.