From the Super Mario Wiki
Gururin Knight (グルリンナイト, Gururin Naito) is the Round 7 boss of Wario Blast: Featuring Bomberman!, formed out of the three Madbombers. He attacks by swinging his sword around to hit Bomberman or Wario. When the protagonist is close to defeating Gururin Knight, Gururin Knight throws his sword like a boomerang at them when they approach. In order to defeat him, Bomberman or Wario must approach him so that he spins his sword or throws it, and quickly lay bombs down in his path before his sword stops spinning or returns to him, so that Gururin Knight is hit when they explode. After eight hits, Gururin Knight is defeated, and the protagonist can move on to the next stage.