Level select:
Enter the options screen. Set "Vibration" to "1" and "Sound effects" and "Music" to "0". Then, hold L1 + L2 + R1 + R2 + Circle + Square. The message "Spooky Cat" will appear in the middle of the screen to confirm correct code entry.

Ending bonuses:
Successfully complete the game under the hard difficulty setting. The maniac difficulty setting and a bonus helicopter and will now be unlocked. The bonus helicopter flies, turns, climbs, descends, and shoots faster.

Successfully complete the game under the maniac difficulty setting to unlock a third bonus helicopter, which you can use on any difficulty setting. It has the same top speed and fire rate as the second bonus helicopter, but more armor.