A rather newer item to the series, this one has been around since Smash 4. It's from the Mario series, but instead of a "sword" item shape, it's an obstacle moving in a circular motion, often in Bowser's castles.
Though it is far from my favorite item in the game. Despite the flashy look, the beam sword is a better weapon in my opinion.
But like the beam sword and star rod, it packs a punch when thrown at an enemy.