Cheat: Golden Gun:
At the pause screen, press X, Y, A, X, Y

Unlockable: Arena Mode:
Play through the cooperative missions and acquire multiplayer points by completing five optional objectives.

Unlockable: Characters and Arenas:
Unlock the following by earning the appropriate number of multi player points, earned by completing objectives in co-op mode.
Agent 003: 290 points
Baron Samedi: 50 points
Burn Chamber arena: 370 points
Arena Mode, and Cistern arena: 30 points
Diayato Moscow: 400 points
Egypt Commander: 90 points
Egypt Guard: 180 points
Hezmet Guard: 110 points
Katya Jumpsuit: 320 points
Le Rogue: 260 points
Miss Nagai: 450 points
Moscow Guard: 230 points
Mya: 130 points
Odd Job: 70 points
Serena: 350 points
Serena: 430 points
South Commander: 210 points
Test Lab arena: 160 points

Unlockable: Cheats:
Unlock the following by earning the appropriate number of Platinum Medals, earned by completing objectives in single player mode.
All Weapons: 17 Platinum Medals
Cloak: 13 Platinum Medals
Double Ammo: 7 Platinum Medals
Double Damage: 9 Platinum Medals
Full Ammo: 11 Platinum Medals
Full Battery: 15 Platinum Medals
Golden Gun: 1 Platinum Medal
Improved Battery: 5 Platinum Medals
Improved Traction: 3 Platinum Medals
Platinum Gun: 27 Platinum Medals
Slow Motion Driving: 25 Platinum Medals
Unlimited Ammo: 23 Platinum Medals
Unlimited Battery: 19 Platinum Medals

Hint: Earning Multi Player Points:
To earn multi player points used for unlocking bonus characters and arenas, you'll need to complete optional objectives in the co-op campaign. To view these objectives, select the mission you want to tackle and hit CIRCLE. You'll then be shown what the bonus objectives are. Completing these objectives will earn you 10 multi player points.

You can also view these challenges on the pause menu of a co-op game.

Hint: Loads of Tips:
1) Crouching raises the chance of you not getting hit significantly.
2) Always look for available cover at all times.
3) The Q Spider can unlock secret areas and items by crawling through open spaces and scouting.
4) Never charge into a open space without an automatic gun and a lot of ammo.
5) Missiles are very easy to waste and can't be replenished so use them very sparingly.
6) Don't rely on hand-to-hand combat.
7) Always keep your P99 in reserve in case of emergencies.
8) You are a spy which means you need to be silent, crouch, walk, and silently disable men.

Hint: No Medals With Cheats:
If you activate a cheat, such as the Golden Gun, you will not be awarded a medal for completing the mission, no matter how well you do.

Hint: Regain Health:
Crouch to slowly refill your health.

Hint: Train Chase Dirt Bike:
At the beginning of the "Train Chase" mission, instead of taking a left to Bond's Porsche, turn right into a small room. Inside, you'll find a dirtbike and a slightly different path through the level.