Bloody Machete

The Bloody Machete is a weapon that operates like a mix between a Boomerang and the Harpoon. It is dropped by any weak (<20 defense, <40 damage and <5 silver coins loot) enemy during Halloween with a 1/2000 or 0.05% chance. It can be fired rapidly and has a medium range. Like all Boomerangs, it operates at range, but inflicts Melee damage, so Melee-boosting Accessories and Armor bonuses will benefit it. When thrown, it travels straight away from the player until it reaches its max range, but unlike other Boomerangs, once it reaches this point, it falls straight down. It will continue falling until it hits a solid block or enemy, giving it considerable vertical range.

Trivia
Or it could be the weapon of Dr. Mundo, a character of League of Legends.
 * This is the iconic weapon of Jason Voorhees; the hockey mask-wearing killer from the Friday the 13th Movies.