Adam's attack are very powerful -- stay away from him. First, turn the gas pipes on by looking for a console that has a diagram of them. Look around the room to find a smaller A & B console. Look carefully and you will see the gas pipes. Shoot ADAM five times rapidly and he will stop. Then, shoot the pipe. After you hit him, run as fast as possible because he will run after you very quickly. You will get damage no matter what, but you will have to repeat the whole thing again to kill him.
Debug mode (PAL version)
Hold R1 + Square and press Start during game play.
Defeating Gladiator
You can only use the handgun you cannot use Health Packs or Adrenaline. There are five circular plates on the floor. Stand on one and a lighting bolt will hit it. It can cause damage to you. However, if timed correctly, you can lure Gladiator towards you and jump out of the way, allowing the bolt to hit him instead.
Defeating Greywolf
You can easily defeat Greywolf on the roof of his hideout by using Proximity Mines. Just place one near where you enter the roof, and as he circles around he will set it off taking a large amount of life. Just be careful not to set it off yourself. When your mines are down to one, start sneaking behind him then take a few shots and head for cover. Use the one mine you saved for when he gets low on life, because he will back himself into the gap in the corner directly across from the entrance and stay there shooting nonstop. Place a mine in that area beforehand and when he goes there he will set it off, dealing the final blow.
Defeating Ramirez
To defeat Ramirez the second time, you must get up and shoot out the lights. He will then only throw grenades. Next, get up close and shoot him to kill him.
Shoot out the lights first, but since Ramirez has a powerful gun, run behind one of the containers. If you have a good view, you will see him point his gun away from you. This is your chance to attack. Give him everything you have for a moment, then duck back.
First, shoot out the lights. Grenades thrown hard work well sometimes and can possibly take out all four lights at once. Then, run. Remirez throws grenades in intervals of three. Run, then shoot after you are out of the way of the third grenade.
Defeating version 2 Bosses
When fighting weak Bosses such as Greywolf (the first "real" Boss) and Bruce (the first Boss) in Version 2, stand back and shoot them with your missile launcher. Note: You will get Greywolf very mad doing this -- when he gets to shoot you, he will beat you down with his gun severely.
Door password
To unlock the room on the second floor of the bikers' hideout, enter "1993" as a password.
Expert mode
After completing the game for the first time, you will be prompted to save after the ending credits. Answer "Yes" and the game will start again, but will be marked "V2" when you save. This is a harder version of the game. This can be done again up to "V8".
Killing silently
Sneak up behind someone and press R1 + X to will break their neck kill them instantly. Note: This requires some practice.
Maze in Level 1
Use the enhanced sight to see the invisible barrier. You will be out real quick.
Opening the Star Locker
To open the Star Locker, break Hank Redwood's records in Leila mode, then complete the game once. The Star Locker contains all weapons with unlimited ammunition. Note: You may not be able to complete the game normally if the Star Locker is used.
Ramirez's spiders and door
When you battle Ramirez's spiders, shoot them once then stand over them. Press Action, then guide the spiders towards the door. Press Action again to make the spiders jump at the door. Eventually they will melt the mechanism with their acid blood and you can enter.
Regain health
In the manufacturing section there is a load of boxes to climb if you want to go up to the door and turn on the door below. you have to turn right and you jump over the box at the end of the passage and the crystal will be on the floor.