Mutators
Big Explosions - unlock the Hail Mary Ribbon 100 times - Play a private versus match with boomshots and unlimited ammo or Beast Mode with the Boomer. All explosions will be larger.
Big Head - unlock the Gold Horder medal.
Headless Chicken - automatically available. This will cause any decapitated enemy to run around as if still alive and fire at allies (or players of no enemies remain).
Comet - unlock the Gold Shock Trooper medal. Roadie running will cause you to build up energy which can eventually be released on impact.
Enemy Regeneration - unlock the Silver Aficionado medal. Non-lambent enemies regenerate health.
Flower Blood - unlock the Silver King of Cog medal. All blood effects are replaced by flowers.
Friendly Fire - complete co-op campaign with four players.
Infinite Ammo - unlock the Combat Engineer ribbon 100 times. To do this, start a fresh match with two controllers. Have your guest give your main account all of his money. then build a base, build a turret and then have your guest shoot the turret while your main account constantly refills it until you get the ribbon. It's best to do this on Checkout.
Instagib Melee - play as the wretch and score 200 kills. There isn't an overly easy way to do this but once you get the hang of playing wretch, you can do this in a private match. I played on checkout and by the end, I could make it through the first four waves without failing using the wretch. I recommend that when you die, you start from the beginning though because you'll die less often, giving you more kills per time spent playing.
This mutator gives the player a melee attack that is an instant kill for most enemies except for (possibly) the Brumak and the Lambent Zerker. Your melee will still do massive amounts of damage to them though.
Laugh Track - unlock the Bronze Tour of Duty, For the Horde, I'm a Beast, and War Monger medals. This will cause a crowd to laugh after every kill.
Must Active Reload - unlock the Silver Active Reloader Medal. If you do not perform a perfect active reload when you are reloading, the gun will jam just as if you missed the active reload. You will also jam your gun if you don't attempt an active reload at all.
Pinata - unlock the Gold Investor Medal. When this mutator is activated, rather than automatically getting the points for every kill, you will have to pick up the coins dropped when your enemy dies. Since money in Horde is tied to your points, this means that you also have to collect these coins to make money in Horde.
Super Reload - unlock the Bronze Master at Arms medal. This will give you an even stronger active reload, will reload twice as many bullets as you needed and removes the timer on your bonus so that it only disappears when you switch weapons. I'm unsure of how much damage it does but with a hammerburst, the damage is comparable (or superior) to the silverback.
Vampire - unlock the Executioner ribbon 100 times. Just make sure you are playing with other players and be the player to get the most executions in the match. Can be done Privately. This mutator will heal you when you deal damage but you will not heal normally.
No Ammo Pickups - gets rid of ammo boxes on the map. This is unlocked at the start.
Character Skins
Unlock - Requirement
COG Gear - Level 2
Miner - Reach Level 3
Samantha Byrne - Reach Level 4
Beast Rider - Reach Level 5
Dizzy Wallin - Reach Level 7
Hunter - Reach Level 8
Jace Stratton - Reach Level 10
Theron Guard - Reach Level 12
Clayton Carmine - Reach Level 14
Classic Dom - Reach Level 17
Spotter Reach - Level 20
Classic Cole - Reach Level 23
Flame Grenadier - Reach Level 26
Classic Baird - Reach Level 30
Benjamin - Carmine Reach Level 34
Grenadier - Reach Level 39
Civilian Anya - Reach Level 45
Colonel Hoffman - Reach Level 50
Hunter Elite Reach - Level 60
Anthony Carmine - Reach Level 75
Unarmored Marcus - Finish the Campaign
Golden Gear - Unlock the Bronze War Supporter medal*
Classic Marcus - Unlock the Silver Veteran medal*
Chairman Prescott - Unlock the Silver Allfathers medal*
Superstar Cole - Unlock the Gold MVP medal*
Aaron Griffin - Unlock the Big Money Onyx medal or "Like" the Gears of War 3 Facebook page*
Sniper - Unlock Bronze Headshot medal*
Golden Hunter - Unlock Gold Master-at-Arms medal*
Kantus - Unlock Gold Medic medal*
Mechanic Baird - Preorder with Bestbuy
Commando Dom - Preorder with Gamestop
Savage Grenadier - Preorder with Walmart
Savage Kantus - Preorder with Amazon.com
Adam Fenix - Preorder the Limited or Epic edition of the game
Cole Train - Earned in the Beta
Weapon Skins
Black Liquid Metal - Purchase the Gears of War 3 Season Pass.
White Liquid Metal - exclusive to Epic employees green.
Liquid Metal - Originally exclusive to Microsoft employees, now available through marketing promotions. So far, the only way to get it was through a promotion with Jack in the Box, a Fast-food chain in the USA.
Team Insignia Retro - Bronze Veteran Medal.
Team Insignia Lancer - Silver Veteran Medal.
Team Insignia Hammerburst - Gold Veteran Medal.
Team Insignia Shotguns - Onyx Veteran Medal.
Crimson Omen Lancer - 12 + 2 XBL Gold Card promotion purchase.
Crimson Omen Hammerburst - Welcome to Beast achievement.
Crimson Omen Retro - Welcome to Horde achievement.
Crimson Omen Gnasher - Welcome to Versus achievement.
Crimson Omen Sawed-off - Welcome to Arcade achievement.
Infected Omen Set - Must have purchased the Limited or Epic editions of the game or the Limited Edition controller.
Gold Omen Set - Reach Level 100.
Onyx Weapon Set - Get 6000 kills with any given starting weapon to get the Onyx skin for that weapon.
Chrome Lancer - Don't Hate the Player achievement in Gears of War 1
Chrome Hammerburst - Dirty Dirty Horde achievement in Gears of War 2
Chrome Retro - Domination Achievement in Gears of War 1
Chrome Gnasher - Complete the campaigns of Gears of War 1, 2, and 3.
Chrome Sawed-Off - Unlock any achievement in Gears of War PC.
Golden Weapon Set - Veteran Gear achievement in Gears of War 2 or played an online match of Gears of War 3 between 9/20/2011 and 9/27/2011
Golden Sawed-Off - Commando Achievement in Gears of War 1 if you don't have the full set.
Golden Retro - Gained in the Beta if you don't have the full set.
Flaming Hammerburst - Complete one match by 4/24/11.
Flaming Lancer - Complete one match during the week of 4/25/11.
Flaming Sawed-off - Complete one match during the week of 5/2/11.
Flaming Gnasher - Complete one match during the week of 5/9/11.
Flaming Retro Lancer - Does not exist or is not attainable.