Area 51 Cheats

Gray Alien in multi-player mode
Successfully complete campaign mode under the hard difficulty setting.

Life or Death: Alien grenade upgrade
Search the dead soldier in one of the elevators where Cole starts the level to find a small key. Use it to open the small lockers in the first power conduit pit to find a databank item. It will upgrade the alien grenade so that it will track targets.

Moon Landing Conspiracy
When you reach "Lies of the Past: Checkpoint 4", you will ascend in an elevator. Exiting the elevator, you will see a replica of the Moon's surface, a model of the U.S. space suit, and a shuttle the United States used to reach the Moon. This is in reference to the Moon Landing Conspiracy, claiming that the U.S. never actually reached the Moon, and faked the landing to beat the Russians in the space race. The conspiracy was heavily debated, but ultimately rejected by the majority of opinions. Today, only a few people still claim the Moon landing was a hoax.

Defeating Grays
To defeat Grays that use shields, mutate and fire parasites at them. It will bring down the shields faster than any other weapon in the game.

Defeating the Super Beast
When fighting the Super Beast, rather than running straight at him, run around in a circle. When he gets near an explosive barrel, shoot it. It does more damage then the BBG. Watch out for his plasma shooting arm as well. When you finish, Edgar will talk to you, and you get to see him.

Defeating the Theta
To defeat the Theta easily, first make sure that you have a fully charged Mutagen bar and at least three quarters of your health remaining. There are health power-ups lying around where you fight it. Then, enter the room where he is as a mutant and either fire parasites or melee the Leapers that come after you. Using parasites on the first few to restore your health then attacking the rest with melee works well to keep your mutagen full and also leaves the health power-ups available if needed. Try not to hit the explosive barrels as they will almost certainly kill you instantly. Theta will appear after about four Leaper waves and leap at you. To defeat him easily, fire a few parasites at him then move in close to melee him. Though he is both fast and strong, in your mutant form it is very easy to hit him and dodge his attacks because of how the "mutant vision" slows him down. The only attack should worry about is his jump attack that still deals almost fatal damage, even with the damage reduction of mutant form. If you repeat this process (attacking the Leapers with melee or the parasites when they appear) you will defeat him fairly quickly and still have plenty of health and mutagen remaining for the next level.

Defeating the Super Theta
Defeating Super Theta uses generally the same strategy as defeating Theta except for a few things. It is recommended that you leave at least one shot in your Meson Cannon for him because of how much damage the weapon will do. Do not worry too much if you miss, because he is still very easy. After you shoot him with the cannon, transform into mutant form and attack him with melee if your health is full or with the parasites if it is not. After a few hits he will get angry then leap up onto one of the four cryo-chambers and break it open, releasing the alien amoebas. These things must be meleed because the parasites will not trace them. Wasting the contagion on them will only drain your energy. They are not too difficult to hit in mutant form, because the "mutant vision" slows them down. Also, do not stand underneath the chamber that the Super Theta is breaking open. Afterwards he will drop almost directly underneath and will deal either fatal or nearly fatal damage when he hits the ground if you are there. However, after he does land, move in close and melee him for a few hits. The amoebas will not drop down immediately. After you kill the amoebas, return to shooting parasites and using melee against the monster. When he jumps off of the second chamber, fire your contagion at him and melee the amoebas that appear to refill your mutagen. This is done after the second one because of the sheer numbers of Black Ops that you fight before him may have severely drained your health. You may want to use the parasites to refill it. If this is not the case, feel free to use the contagion after he breaks the first chamber. After you use the contagion, repeat the process of melee and parasites until the monster dies. At the absolute longest, the fight should take about ten minutes.

Arcade cabinet
In the earlier stages of the game, there are a few cabinets of the original Area 51 arcade game, complete with red and blue light-guns.

Interesting scans
During the training levels, scan everyone that you can. You will find some interesting equipment of the MPs, including adult diapers and condoms. Hold [Down] until your scanner stops moving and you appear to be looking at your feet. You can now scan yourself and see information about Cole.

Masons and the Illuminati
Shortly after meeting Dr. Cray, you will reach an infirmary where you will find clones of Mr. White walking around, mumbling, and rambling on. On the back of their lab coats you will find a Masonic lodge (a symbol of the Free Masons) suggesting a connection between the Masons and Illuminati.