Pause game play, then press 1 eight times.
Hint: Graveyard: 100,000 points:
Survive for in the Graveyard level without the Boss appearing by not killing too many enemies. You will get 100,000 points and it will turn into night.
Hint: Alternate El Doba:
Defeat El Doba in any level before he can shoot ten times. Then, do not lose any lives in the next level. When El Doba appears next, he will resemble a schoolgirl that can shoot faster.
Hint: Bonus points:
Have your score have a value of "0", "1", "4", or "5" in the hundreds position at the start of a level. Wait until the third enemy of the level appears, then hit it with your first shot. Do not shoot anything else before this. A new character will appear on the top of the level and you will get 10,000 points.