Enter the "Extras" menu and select "Promotional Codes". Then, unlock the following functions by entering the corresponding codes:
CHEAT FUNCTION - CHEAT CODE
Eye of Ra ASE - EYEOFRA
Golden Destroyer (online) - 14KARMOR
AR-C Eclipse hint:
With the AR-C Eclipse (the gun that can turn you invisible), before turning invisible for getting past turrets or enemies, shoot the gun until it is almost overheated. Then, charge it up so you become invisible. The gun needs time to cool down before lowering its temperature below zero. This lets you remain invisible for longer. If you need to shoot for long periods of time, turn invisible until the temperature is almost at its minimum, then start shooting to keep firing for a longer time.
"Green Ooze" achievement hint:
During the Washing D.C. level, go to the trailer and fall down the ladder to the sewer. After killing to two mites in the room, aim your reticule at the canister of Green Ooze with tiny footprints going into the sewer water to unlock the Green Ooze Achievement. Note: there's also a Conspiracy Object in that room).
Dark Star Armor Upgrades:
To unlock Dark Star and a few armor upgrades, walk in a circle in the main room of Atlantis with ASE and scan all the items that can be scanned.
Hive Cannon Blueprints hint:
Take the Conduit from the Atlantis hub program to take you to Oxford University. Upon arrival, look to the right to see a rock pillar that you can jump to. Jump to it and in the middle of it will be a scannable object. Use the ASE to receive the blueprints for the ever-useful Hive Cannon.
Invasion Mode Credits hints:
Invasion Mode (under Splitscreen on the main menu) is an excellent way to earn tons of Credits. The following strategy will earn you about 30,000 credits per hour. First, you'll need the following: Windowmaker Turret, Windowmaker Turret specialization, and a secondary Weapon you can use to take out enemies (the MP5 or HVS). Also recommended are; Metal Legs, Quickness, Frag Grenades, Improved Ballistics Damage.
This strategy is about finding a corner where enemies cannot spawn directly next to you in and setting up your automatic turret to pick them off easily. It works best in Siberia, but can be done on any map. Find a spot on the map with the following: no enemy spawn points directly next to it, a safe spot you can duck into when your health gets low, cover, and a clear angle on enemies. There's one corner of Siberia down a hill where your Turret automatically takes down enemies right as they spawn. Just let it fire and use your secondary weapon to take down the ones it isn't shooting. Take an enemy SCAR or Hive Cannon at some point and be sure to chase after the Big coins (1,000 coins is what you get from an average 10 minute WiFi match) and bonus caches.
This strategy is guaranteed to work for the first 3 or 4 waves. Watch out for the following; Robotic Dogs attacking your turret, Skimmers (the flying guys, your turret can't take those out), anything with Explosives, especially those SMAW guys), and the suicide bombers. You'll make a quick 10k-30k credits if executed correctly.
Widowmaker Turret Blueprints location:
In Siberia, when you see the science lab, head through the row of doors on your right. Once inside the science lab, take the last door to receive the blueprints.