Hint: Bypass level 1 Boss:
Hover at the top right corner of the screen when the Boss appears and wait. The Boss will eventually fly away, resulting in an easy victory.

Hint: Defeat level 4 Boss:
Note: This trick requires at least three extra lives. Ram into the Boss three times and sacrifice three lives. Then, rapid fire into the Boss with your last ship for approximately ten seconds. A bonus level will appear after he is defeated.

Hint: Bypass other Bosses:
Hover at the top left corner of the screen when the Boss appears and wait. The Boss in most levels will eventually fly away, resulting in an easy victory.