To easily defeat the ninja at the end of the level, first get and keep the Screaming Cannon. While fighting the ninja, stand with your back to the elevator door that you came through. The ninja will teleport and get stuck in the elevator behind you. Walk forward, turn around, and you can then see him trying to run through the door. Shoot him with the Screaming Cannon and he will die instantly. Note: Sometimes he will teleport beside you. If this happens, hit him until he has to teleport and try standing in front of the door again.