Allow the game to reach the title screen, then reset the NES console. Then, press Right, Left, Right, Left, A, B, A, B when the title screen appears again.
View next Boss:
Kill the first Boss and pause game play as he leaves the screen.
1000 point bonus:
Locate the red flower in level 1-4. Shoot the coyote that attacks from behind twice while jumping to display a power-up in the form of a Nintendo controller. Get the controller to collect 1000 points.