Unlimited Super bombs
Press Square(2), Right, Down(2), Left, Square, Triangle at the title screen. A sound will confirm correct code entry.
Machine gun
Press Right(2), Square, Triangle, Right, Left, Down(2) at the title screen. A sound will confirm correct code entry.
View FMV sequences
Press Triangle(2), Down, Square, Up(2), Left, Triangle at the title screen. A sound will confirm correct code entry.
Infinite lives
At the title screen, press Up, Down, Left, Right, R1, L2, R2, L1. If you entered the code correctly, you will hear the sound of a tone.
Level select
At the title screen, press Down, Left, R1, R2, L1, L2. If you entered the code correctly, you will hear the sound of a tone.
Hidden character
At the title screen, press Up(3), R1, L1, R2, L2, Down. If you entered the code correctly, you will hear the sound of a tone.
Keep Good Weapons
Always keep your eye on your Health Meter. If you are about to die, equip your most undesirable weapon. When you die, you'll only lose the weaker weapon and keep your more desirable ones.
Smart Bombs
You can only carry five Smart Bombs, so use them sparingly. Don't waste them on a mid-boss. Save the bombs for the big bosses.
Patience
Sometimes the best boss strategy is to slowly pick away rather than go full on. The game doesn't give you a lot of lives, so try to be extra weary when fighting bosses.