Health at 100%:
In the mission where you chase the female assassin (mission 3) Thames Chase, when you are defusing the bomb, stop the clock on exactly 0.07 seconds left and your health will be topped back up to 100%.

Bye, Bye Helicopter:
I found a useful strategy for destroying the attack helicopter on City of Walkways 2. First, kill the guy on the box with the Rocket Launcher, (00 Agent only), with the Meyer TMP, or the Wolfram P2K, so he doesn’t blow you up while you’re doing this. Go to the car on the lower level, and pick up the Sentinal and some ammo. Then, go over, (on the same level), and stand in the spot where you can pick up more Soviet ammo. Aim the Sentinal through the gap between the ramp and the upper floor. From here, you should be able to see the helicopter when it pauses its movement. Shoot it with the Sentinal during this pause. Eventually, the helicopter will blow up, (if you hit it). (NOTE: It’s not a good idea to use this hint if you’re trying to get Wildfire Mode in Agent. Usually, the final mission time using this hint is about 8-10 minutes.)

There’s an easier way:
On mission 12, Fallen Angel, after you enter the finger-print-locked door, don’t move. Take out any gun but the Soviet, (since it’s not that accurate), and shoot the two security cameras, (one on the far right wall, and one on the closer left wall). After that, just run over to the stairs, and the doors will not close and no gas will spray out.

Extra 9mm Ammo:
If you happen to like the guns that use 9mm ammo, here’s a way to get some extra. With any guard on any level, use either the Stun Bomb or the Stun function on your wristwatch to stun an enemy. After they drop their gun, wait until they pull out a Wolfram P2K. Kill them, and you’ll have some extra 9mm ammo.

Defusing the bomb on the London underground level:
When defusing the bomb on the London underground level, start to defuse it has normal but don’t finish until the timer has reached 7 seconds left. Defuse it now to recieve full health.

Instant kill:
When playing with AIbots in the frostbite multiplayer level I found this VERY fun and usful cheat. First set the weapons to sniper combat and begin play, go across the twin bridges in the area that has the log cabin. Once there sit and wait computer players should start running across the bridge, when they do shoot the ammo box for an instant kill (the comps will never learn)

An Easy Ride:
In mission 7 “Midnight Departure” eliminate Davidov as quick as you can. Pick his stuff up and if you’re on secret or oo agent get the ID badge from the shack in the woods. Get back on the main path and don’t let the alarm get pulled. The first truck you see after you cross the bridge(kill the three guys on the right side of the truck.) Then climb in the back of the truck(wait a few seconds for the truck to start) and then the truck will take you to the air field.(This works on all difficulties and is great for the cheat.)

A Quicker Way:
I really liked this cheat and I hope you like it just as much In Mission 1 “Courier” right at the start of the mission go to the safe-deposit box is is and set of the alarm and then get the flash bang gun and the apointment card and run out the front door (it works on all difficulties and is great for the cheat on secret agent difficulty)

A.S.S ESSENTIAL:

When in multi-player mode choose the level called FROSTBITE. Then go across the bridge with the bodyarmor and turn until you are facing the wall, walk and drop down. facing the cave turn left. There should be a small cave go in and keep walking there will be two boxes one an A.S.S ESSENTIAL the other some ammo. Continue up till you reach flat land turn right and you will be at a lookout point. To get down just run and drop.

Unlock extra stuff:
Beat the following levels under the specified time to unlock multiplayer levels and more skins: