CheatCodes.com has all the official Metal Gear Solid: Peace Walker PSP cheats to unlock everything. If you know of any that we don't have, please let us know.
All published and official codes as of Wednesday June 19, 2013 for Metal Gear Solid: Peace Walker are shown below.
In the Pupa Battle at the end of the first chapter you fight this large AI weapon. How I defeat the Pupa is I have only recovery items on the right side of the backpack thing and I have a "RPG2", a "FIM-43" and a supply mark of any kind (you will need this). When in the arena keep shooting at the AI Pod until it falls down. To dodge its main attacks like the charge just lay down and the machine guns/charge beam just keep walking to the side while shooting at it. Keep shooting and using the supply mark when you run out of ammo. Always have a health-recovery items in use. When its completely out of health shoot the AI pod with one of the launchers and enter it before it gets back up. On the inside of the Pod there are a lot of discs that control it. Pull out as many as you can (take out column by column, its faster) and make sure you get a lot out before the time runs out. Once the time runs out it will skip to a cut-scene where Huey and Snake meet and the Pupa dies. It took me around a month to come up with this strategy and it works almost every time once you are used to it.
In the 'Infiltrate The Crater Base' at the end there will be an interactive cutscene where you have to find the right truck to complete the mission, pick the truck with the license plate that reads 'Centro America 63824 Peace Sentinel' and Snake will find Mr. Kojima. After the misson if complete he will be recruited, he has S-rank Medical and Intel skills.
To unlock the Monster Hunter Ops you must first listen to All of Chico's briefings, then you must go to Extra Ops 29 and go to the beach (La Playa) and go to the pier with the Cat. A cut-scene will occur and the Op will end, afterwards you will unlock Extra Ops 121 Note that the monsters are hard and to get S-rank on each you must Not Kill A Single Creature, even the Main Boss, only Tranquilize them.
To defeat the cocoon you must have a RPG-2 and a PKM. At the begining go all the way to the right and climb up the ladder. Once you go up you will see two front walls. Go to the 2nd one. There the cocoon can't shoot you with the front missles and machine gun. There you will hit the cocoon's head with the RPG-2 first. Then shoot him with the PKM as long as you can. The heat-seeking missles will smash through the wall so try to move around and then go back after the missles are fired. When the cocoon is almost dead it will dishock a ladder climb it to the top. The head will be in front of you depending on which side you climb. Hit with all you got. That's how you win.
While playing the game you can either knock out the patrol guards or put them to sleep with your tranquilizer gun (I recommend putting them to sleep). When they're out walk up to them, go to your Items and select the Fulton Recovery System (the air balloon looking things) press the action button and Snake (aka Big Boss)will attach a pack to the enemy, a balloon will come out drag the enemy up in the air and Miller will then say that the extraction was a success, this is how you add more people to your staff at Mother Base for your Combat Squad, Research and Development team, Medical Squad etc. You can also use the Fulton packs on hostages and enemies that are bleeding out (I don't recommend doing this until you have the Sickbay available so they can recover). So yeah do this to expand your staff if you are in need of stronger weapons and items.
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