Beat Cunningham on ANY difficulty by stamina kill and beat the game before January 1st 1971 in game. You get him after you make a new game.
Defeating Cunningham
Use Snake (he has the most health and stamina, and dying with him will not cause loss of your favorite soldier) with the 5.56x45mm Caliber Assault Rifle (M16A1 or XM177E2) and RPG7; Body Armor; and Medical Kit (L). Fire the M16A1 using the L lock-on button. Fire two or three magazines into his flying machine and there will be a minor explosion. He will drift downwards as his flying machine malfunctions. At this point, fire using the L lock-on again, but keep it to short bursts or single shots. Almost every shot will count towards taking down his life. Ammo boxes for the 5.56 rifle will continuously appear as you run low, and there is a spare M16A1 rifle as well. The rest is standard bullet dodging. Note: You can fire at the rockets he shoots later as his health gets low by shooting at them in First Person mode. Firing at the mines he throws will cause them to explode safely at a distance. Also, RPG7 rockets will count as a bullet hit on his health, and two or three consecutive shots will cause the flying machine to drift down faster, but there are no RPG refills during the battle.
Defeating Null
The times which you can shoot him with a non explosive are when he is reloading, turned his back against you, still looking for you, or sometimes while shooting if you are lucky. The best gun for this is the shotgun. When you actually get a shot into him, it will knock him down.
CQC of any kind does not work on Null. If you try to punch, kick, or tackle him, he will slash you with his sword. He will also block any bullets you shoot at him. The only way to defeat him is to hit him in the back or wait until he reloads his gun. He fires three bursts before having to reload, and will shoot even if he cannot see you. Wait until the third burst, then quickly jump out and shoot to kill or tranquilize him. Alternately, use any type of explosive, as he cannot block them.
Defeating Python
When fighting Python, lock on to him with L and shoot him when he becomes visible through the fog. Make sure to continuously back up, otherwise he will lunge forward and knock you down with his weapon. It is also a good idea to plant the TNT with a soldier other than Snake. By doing this, when you begin the fight you will start as the character you planted the bomb with. Then if your character dies, you will have the option of selecting the next player to fight with so that you can save Snake to finish the job after Python has been weakened.
The best weapon to use against Python is the shotgun. It will knock him down and you can shoot him again before he gets back up. Additionally, the shotgun deals a lot of damage but does not require you to do any fancy moves.
Easy reload
Have two weapons equipped. When you are close to running out in your clip, change weapons then immediately change back and your gun will be reloaded.
Elisa
Get a Medic level of 80.
Eva
Enter "E.APPLE" as a password to unlock Eva.
Extreme Difficulty
Beat the game.
Frequency for doors
During the mission before the Cunningham fight, the frequency for the first frequency door is scratched on the wall behind the guard that is posted in the room.
The frequency code for the doors at the Silo Complex are 145.75 for the first and 148.51 for the second.
Gako soldier
Enter ! TRAUMER as a password. In the European version of the game, enter GAK.O as a password.
Gene
Recruit 200 soldiers and stamina kill Gene all in one playthrough.
Major Zero
Have a MGS:DGN game save on your psp's memory stick. (Second Playthrough only)
Null
Kill Null by stamina kill or HP kill when you face him twice and beat the game. You get him after you make a new game.
Ocelot
Enter "R.R.R." as a password to unlock Ocelot.
Para Medic
Contact her on the radio on the Comm Tower stage. She will later need to be resceud in the hospital stage. Place spies in the hospital.
Python
Kill Python by stamina kill.
Raikov
Place spies in Western Wilderness before clearing the Guard House mission. Afterwards you should get a report of a handsome prisoner being held there.
Recruiting soldiers
If you are looking for soldiers to recruit the Soviet Patrol Base is an easy place to capture them all.
To recruit multiple soldiers at once, drag several of the enemy soldiers over to one of your teammates while they are hiding in a box. Then call the prisoner evac frequency and your teammate will capture all of them.
Sigint
After Snake is captured and rescued you can contact Sigint on the radio at the Comm stage. He will need to be rescued in the town.
Sokolov
Give the Saturn V blueprints to Sokolov.
Stealth Camouflage
Beat the game with your Technician status level at 99.
Teliko
Have a MGA game save on your psp's memory stick. (Second Playthrough only).
Ursula
Enter PK +ESP as a password. Note: You cannot unlock her and Elisa at the same time. In the European version of the game, enter ESP:ASP as a password.
Venus
Have a MGA 2 game save on your psp's mamory stick. (Second Playthrough only)
