The Horseman's Blade

 is a sword dropped by the Pumpking, a boss monster in the Pumpkin Moon event. When an enemy is hit, a homing pumpkin head will appear. To create a swarm of homing pumpkins, one can easily kill statue spawned mobs (e.g. Bunnies from Bunny Statues).

Trivia

 * The Horseman's Blade and its homing pumpkins are a reference to The Legend of Sleepy Hollow, in which the main character is chased by his enemy masquerading as the Headless Horseman, who throws a pumpkin at him.