Successfully finish the game in Standard or Training Mode with the best ending and after the credits a reward screen will pop up informing you that you've received bonus costumes. Save your game data, then load it for a new game and you'll have a special key in your inventory. This can be used now to open up the Dressing Room. Note that in Advanced Mode you do not need the special key to get the costumes, you can enter the room automatically.

Have your character aim directly at the television screen, and then aim up as you fire. You must fire in mid-motion as your character raises their arm. If you perform this perfectly, you can actually crack the game screen temporarily.

highlight advanced and hold down right until it goes green then when you pick up a clip of 15 bullets you will get 30

Successfully finish the game in under three hours with any ending. A screen should pop up telling you that you've received the weapon. Then save your end game data, load it for a new game and you will have it in your inventory automatically.

There are three different types of endings for each character; good, OK and bad. The type of ending you get depends on how many characters you managed to get to the helicopter alive at the end of the game. If you defeat Tyrant and make it to the copter with your character, your partner and (depending on who you're playing) either Rebecca or Barry you will get the good ending. If you forget to rescue your partner from the jail cell and make it to the copter with either Rebecca or Barry, you'll get to OK ending. And if you somehow forgot to both rescue your partner AND let Rebecca or Barry die, you'll get the bad ending.

Complete the game with any characters in Advance Mode, saving all your partners. Then the unlimited Magnum will be stored in your inventory in the next scenario you saved.