Press Up, Down, Up, Down, Left, Right(2), Y, X(2) at the main menu with the "New Game" option. A scream will confirm correct code entry. Then, press Down at the "Press Start" screen until the level selection option appears.
Every type of weapon has five disarms (B, Up + B, Left + B, Right + B, and Down + B). An exception is the shotgun, which B and Up + B. Note: Disable the "Random Disarms" option or you will not learn any new ones.
The disarms are held by one enemy on each level possessing guns. Go through the levels, disarming everyone possible. Keep tabs of who you were able to disarm in a particular room before you die. When you continue, you will know which ones are remaining to disarm until you check everyone. Then, move on, save, and repeat. There is a shotgun disarm on mission 2 after the Boss. There are fuve disarms for all weapons, including the shotgun. The enemies will only unlock disarms for the weapons they are using, and of course there are no disarms on the levels without guns. Always use cover, duck behind something, or wait around a corner and be patient. Eventually, they will approach closer. Press one of the B combos their fate is sealed. Draw them closer one by one and disarm them or take them hostage systematically, while never exposing yourself. The objective is to not get shot, or go down in a blaze of glory
On the ''New Game'' screen, just after the ''Press Start'' screen, hold L + R and press Y, X, Up(3). A message will confirm correct code entry. This mode has unlimited shotguns.
Unlock All Chapters:
Press U, D, U, D, L, R, R, Y, X, X on the "New Game" screen after the "Press Start" screen to unlock all chapters in the game.
To unlock the mini-games, successfully complete the game under any difficulty setting.
Destroy GAC easily:
All you have to do in chapter 15 where you have to destroy the GAC chopper is to kill any of those GAC units around your view especially the one far down shooting a bazooka. The M4 machine will do the trick. Continue to murder any GAC unit in sight until the chopper stops sending them. Whatever you do, do not go upstairs or you're dead meat! As soon as the chopper stops sending fools, pick the grenade launcher any any gun you can, walk about three steps toward the water fountain until you're standing on a gray diamond, manual-aim the chopper and empty all your bullets in that chopper. Continue this unitl you're stuck with Shadow or a shotgun. Pick up any ammo around and empty them all into the chopper. You will eventually run out of ammo, but walk to the stairs on you left and crouch. A GAC unit will come running down. Let shadow waste him and get his gun. Then to your right, there should be a pistol up the stairs. Run quickly and get it. Return back to the gray diamond and empty your guns. If you run out again, do the same shadow trick on the right side of the stairs. That should send that chopper down. I tried every other way and I was toast so this was the best way and it only took 5 minutes.