1how it flies
It goes out flat, loses momentum, and drops on the way home, so the return leg travels a lower line than the throw did. Against something standing on the same ground as you, that second half often misses entirely. It works best thrown slightly upward at a target above you, or into a corridor where a wall turns it around early and it comes back on a useful path.
farming one
It only exists during the Halloween window and only comes off the weakest enemies in the world, so the fastest approach is whatever produces the most bodies per minute. A goblin invasion qualifies almost end to end. A blood moon with spawn boosters running does the same job on an ordinary night. Farming tough enemies for it is wasted effort, because they are the wrong pool.
where it comes from
The design is Jason Voorhees, hockey mask franchise and all. He swings his. Yours leaves your hand and comes back.