There is a bonus stage after stage 1, 2, 3 and 4. The objective of each bonus stage is simple: shoot all ninjas!

Enemy ninjas will keep leaping up the walls as you fall down. You have to keep throwing shuriken to kill them (they only take one hit each to kill) and need to try and kill them all to receive a bonus of some kind. As the bonus stages goes on, more and more ninjas will appear, until you reach the ground. As a general rule, if you stay to the left of the screen and keep shooting, you'll have a greater chance of hitting all of the ninjas.

Depending on how well you do you will receive a bonus at the end. If you shoot several ninjas, you'll just get points bonuses, but if you manage to nearly get them all you'll receive extra lives instead. If you manage to kill every single enemy ninja, 3 extra lives will be yours.