Successfully complete the indicated task to unlock the corresponding weapon:
Desert Eagle, Long Barrel: Get the Fox Emblem.
Patriot Future Assault Weapon : Successfully complete the game with a "Big Boss" rank. This weapon has infinite ammunition.
Race Gun pistol: Successfully complete the game in Single Player mode.
Solar Gun: Collect the five statues (the four Battle Beauties and Frog Soldier/Haven Troopers) with non-lethal means on their respective idols.
Thor 45-70: Get the Fox Hound Emblem.
World War I pistol: Get the Hound Emblem.
Bonus ammunition
Successfully complete the game to unlock the following ammo for purchase from Drebin:
Emotive Cry
Emotive Laughter
Emotive Rage
Emotive Scream
Smoke Grenade Blue
Smoke Grenade Green
Smoke Grenade Red
Smoke Grenade Yellow
Bonus equipment
Successfully complete the indicated task to unlock the corresponding piece of equipment:
Bandanna: Successfully complete the game in Single Player mode without killing anyone, including Bosses. Alternately, purchase it from Drebin for 5 million Drebin Points after starting another game session after completing the game. This item gives you infinite ammunition.
Digital Camera: It is found in the Nomad vehicle during the mission intermission. Note: It will contain bonus photos if you wait until Act 4 to get the camera.
Scanning Plug S: Log more than ten hours of online play time on the same profile as your single player game to unlock it for purchase from Drebin.
Stealth Item: Successfully complete the game in Single Player mode without instigating an alert. Note: You can trigger a caution.
Bonus face paint
Successfully complete the indicate task to unlock the corresponding face paint:
Big Boss: Get the Big Boss Emblem. When you wear this mask, it causes enemies near you to cower in fear and/or run away screaming.
Crying Wolf: Defeat Battle Beauty (human form) Crying Wolf by non-lethal means.
Drebin: Acquire and keep over 60 weapons.
FaceCamo: Defeat Battle Beauty Laughing Octopus. This mask functions like the Octocamo suit, but just on your head.
Laughing Octopus: Defeat Battle Beauty (human form) Laughing Octopus by non-lethal means.
Metal Gear Solid Snake: Start the Shadow Moses level.
Otacon: Shock or run into Otacon at high speed with Metal Gear Mk. II during an interactive mission brief.
Raging Raven: Defeat Battle Beauty (human form) Raging Raven by non-lethal means.
Raiden A: Shock or run into Sunny at high speed with Metal Gear Mk. II during an interactive mission brief.
Raiden B: Shock or run into Naomi at high speed with Metal Gear Mk. II during an interactive mission brief.
Roy Campbell: Shock or run into Campbell at high speed with Metal Gear Mk. II during an interactive mission brief.
Screaming Mantis: Defeat Battle Beauty (human form) Screaming Mantis by non-lethal means.
Young Snake: Start the Eastern Europe level.
Young Snake with bandana: Start the Eastern Europe level.
Bonus costumes
Successfully complete the indicate task to unlock the corresponding costume:
Altair's Rags (Assassin's Creed): Get the Assassin's Emblem.
Business Suit: Successfully complete the game.
Civilian clothes: Start the Eastern Europe level.
Metal Gear Solid optical camo: Successfully complete the game in Single Player mode without going into alert phase. Alternately, purchase it from Drebin for 5 million Drebin Points after starting another game session after completing the game. This camo makes you completely invisible.
Middle East militia disguise: Go to the Middle East militia safe house.
South American militia disguise: Go to the South American cove valley village.
iPod songs
Successfully complete the indicated task to unlock the corresponding song on Snake's iPod. Certain songs have an additional secret effect when played during the game.
Beyond the Bounds: In Act 4: Shadow Moses, Tank Hangar, after power is restored, return to the upper catwalk, and explore all the rooms. This song increases stun damage done by Snake from non-lethal weapons.
Big Boss: Get the Big Boss Emblem. This song increases stun damage and Snake's accuracy.
Bio-hazard: In Act 3: Europe, Midtown, hold-up a resistance soldier and body search him. This song causes soldiers held by Snake to scream.
Destiny's Call: Received randomly from an allied or neutral militia or rebel soldier after Snake gives them a healing item. This song causes soldiers held by Snake to become enraged.
Flowing Destiny: In Act 4: Shadow Moses, Canyon, before leaving the canyon area, examine the rocky walls for a hole hiding the song. This song causes soldiers held by Snake to weep.
The Fury: In Act 2: South America, Cove Valley Village, search inside the fire-ravaged house. This song causes soldiers held by Snake to become enraged.
MGS 4 Love Theme/Action: Received randomly from an allied or neutral militia or rebel soldier after Snake gives them a healing item. This song causes soldiers held by Snake to weep.
Opening - Old L.A. 2040: In Act 4: Shadow Moses, Nuclear Warhead Storage B2, input "78925" into Otacon's lab computer. This song increases Snake's accuracy.
Policenaughts Ending: In Act 4 Shadow Moses, Nuclear Warhead Storage B2, enter "13462" into Otacon's lab computer. This song causes soldiers held by Snake to fall asleep when touched.
Rock Me: In Act 2: South America, Confinement Facility, search the island in the south-eastern quadrant. This song increases the amount of life recovered from items and other means.
Sailor: In Act 2 South America, Vista Mansion, look between the east wall and a cargo container. This song increases the amount of life recovered from items and other means.
Show Time: Received randomly from an allied or neutral militia or rebel soldier after Snake gives them a healing item. This song causes soldiers held by Snake to scream.
Snake Eater: Get all 40 game clear Emblems. This song increases the amount of life recovered from items and other means.
Subsistence: Play one game of Metal Gear Online, starting the match with at least two players. This song increases Snake's accuracy.
Emblems
Successfully complete the indicated task to unlock the corresponding Emblem:
Ant: Shake 50 enemies for items.
Assassin's: Successfully complete the game in Single Player mode with killing more than 50 enemies with the knife, having over 50 CQC holds, and getting discovered less than 25 times.
Bear: Choke 100 enemies to death.
Bee: Use the Scanning Plug S or Syringe on 50 enemies.
Big Boss: Successfully complete the game in Single Player mode on the hardest difficulty without dying, instigating no alerts, killing no enemies (including Bosses), using no life recovery items, using no stealth suit or bandanna special items (can possess, but not activate), and with a completion time of less than 5 hours.
Blue Bird: Give friendly soldiers 50 items.
Eagle: Get 150 headshots.
Fox: Successfully complete the game in Single Player mode on the Naked Normal or higher difficulty without dying, instigating no more than five alerts, killing no enemies (including Bosses), using no life recovery items, using no stealth suit or bandanna special items (can possess, but not activate), and with a completion time of less than 6 hours.
Fox Hound: Successfully complete the game in Single Player mode on the Big Boss Hard or higher difficulty without dying, instigating no more than three alerts, killing no enemies (including Bosses), using no life recovery items, using no stealth suit or bandanna special items (can possess, but not activate), and with a completion time less than 5 hours and 30 minutes.
Frog: Dive or roll 200 times.
Gecko: Press against walls for a total of one hour.
Giant Panda: Successfully complete the game after 30 cumulative hours of game play.
Gibbon: Hold up 50 enemies.
Hawk: Be admired by 25 friendly soldiers.
Hog: Get 10 combat highs.
Hound: Successfully complete the game in Single Player mode on the Naked Normal or higher difficulty without dying, instigating no more than three alerts, killing no enemies (including Bosses), using no life recovery items, using no stealth suit or bandanna special items (can possess, but not activate), and with a completion time less than 6 hours and 30 minutes.
Hyena: Pick up 400 dropped weapons.
Inch Worm: Crawl on the ground for a total of one hour.
Little Gray: Collect all 69 weapons.
Lobster: Crouch for a total of 2 hours and 30 minutes.
Rabbit: Look at 100 Playboy pages.
Password option
Successfully complete the game in Single Player mode to unlock the "Password" option in the "Extras" menu. There are no known passwords currently, but keep checking back.
Bonus combat vests
Successfully complete the game in Single Player mode to unlock new combat vests.
Big Boss Extreme mode
Successfully complete the game in Single Player mode to unlock the Big Boss Extreme difficulty.
Replay bonus
Successfully complete the game in Single Player mode, and create a cleared saved game file. Start another game session, and encounter Metal Gear II in Act 1 to get the Drebin Points, weapons, ammunition, items, and special items from your original game.
Alternate ending
If you fight Mantis with a Sixaxis controller, the ending is different than if you were using a DualShock 3 controller.
Otacon bonus
In Act 4: Shadow Moses, when at Otacon's office, he will ask you for the code. Input "14893" to hear the familiar monkey sound and get 100,000 Drebin Points points. Note: This is a reference to the Codec frequency (148.93) that Drebin calls you on. Alternately, input "78925" or "13462" as a code to get an iPod song.