Go through the first level, and do not destroy the Boss. Finish the rest of the game to see the failed ending.
Extra Continues
At the title screen, hold Up+L+R and then press start.
Make The Napalm Gun upgradeable
Clear Level 2 without shooting or hitting anything execpt the boss.
Napalm Gun
To get the Napalm Gun, all you have to do is complete the first level WITHOUT SHOOTING ANYTHING EXECPT THE BOSS OF THE LEVEL. However, you DO have to complete one more task before it stays with you for the whole game: you MUST complete level 2 WITHOUT DYING. If you can complete level 2 without dying, the congratulate yourself on a job well done; you now have the most powerful weapon in the game.