GameWorld

Toasty :
In act 4, "The Hive", chapter 5, "The Best-Laid Plans" right after rejoining with Dom (or Marcus if co-op) walk all down the hallway to where the locust ammo boxes are. There is a pedestal in the center along the wall. Shoot it with and press "X". Be prepared for toast.

Everyone is a Cowboy :
Start at the beginning of Act 1 Chapter 3 "Rolling Thunder" on Insane difficulty. At the start, before the cutscene, there are 3 cowboy hats. Use your pistol to shoot them. Remember to press BACK to skip the dialog.

Make sure you are facing the direction the rig will be moving in. The first hat is on the side of the building behind and to the right of the rig.
The second is between the front wheel and back wheel of a tank sitting to the left of the rig.
The third is behind the second large gas tank next to the tank with the previous cowboy hat.

If you do manage to shoot all three, here's what you'll get:
All characters on the rig will immediately equip cowboy hats.
In the next chapter, if you fail kill the driver of the hijacked rig in time, when you see the cutscene of your rig falling into the ravine, you will see a cowboy hat floating down to earth.
If you succeed in killing the driver of the hijacked rig, he will be wearing a cowboy hat.
During the cutscene where the hijacked rig falls into the ravine, you will see a cowboy hat falling down to earth.
A corpser that emerges from the ground later in the chapter will be wearing a cowboy hat and screaming "YEE HAW!"

Golden Shotgun :
Achieve the highest rank in online multiplayer mode in order to unlock the Golden Gnasher (Shotgun)

Golden Pistol :
Unlock 1000/1000 Gamerscore points and get to rank 5 in online multiplayer to unlock the Golden Snub pistol.

Insane difficulty :
Complete the game once to unlock Insane difficulty.

Unlockable Gamerpic :
Clear campaign mode on Insane difficulty to unlock a bonus gamerpic.

Another Unlockable Gamerpic :
Earn the Friends with Benefits achievement (Complete all acts in Co-op on any difficulty) to unlock another bonus gamerpic.

Even more Gamerpics :
Complete Seriously 2.0 to unlock an additional Gamerpic.
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Unlockable Multiplayer Skins
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Anthony Carmine :
Successfully complete Act 1 in the original Gears Of War.
Dizzy Wallin :
Successfully complete Act 1 in Single Player mode.
Flame Grenadier :
Successfully complete Act 4 in Single Player mode.
Kantus :
Successfully complete Act 2 in Single Player mode.
Lt. Minh Young Kim :
Find 10 COG tags in the original Gears Of War.
RAAM :
Defeat RAAM in the original Gears Of War on Hardcore difficulty.
Skorge :
Successfully complete Act 5 in Single Player mode.
Tai Kaliso :
Successfully complete Act 3 in Single Player mode.
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Achievements
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Unlockable
How to Unlock

A Parting Gift (20 points)
Kill 10 enemies with a grenade while down but not out (any mode).
And the Horse You Rode in On (10 points)
Story progression in Act 5, Chapter 1.
Around the World, Again (30 points)
Win a multiplayer match on each map (any mode).
Artist of War (75 points)
Complete all campaign acts on Hardcore Difficulty.
Back to Basic (10 points)
Successfully complete the 5 lessons of multiplayer Training Grounds.
Beat the Meatflag (10 points)
Capture 10 meatflags in Submission (public).
Better Wrapped in Beacon (10 points)
Story progression in Act 4, Chapter 3.
Brumak Rodeo (10 points)
Story progression in Act 5, Chapter 4.
Collector (5 points)
Recover 5 collectibles (any difficulty).
Completionist (30 points)
Recover all 41 collectibles (any difficulty).
Crossed Swords (10 points)
Win 10 chainsaw duels (any mode).
Crowd Control (10 points)
Melee 10 enemies down with the Boomshield equipped (any mode).


Dirty, Dirty Horde (20 points)
Survive the first 10 waves of Horde (any difficulty, any map).
Does This Look Infected to You? (10 points)
Story progression in Act 5, Chapter 5.
Escort Service (10 points)
Story progression in Act 1, Chapter 4.
Freebaird! (10 points)
Story progression in Act 2, Chapter 5.
Friends with Benefits (50 points)
Complete all acts in co-op on any difficulty (Marcus or Dom).
Girl About Town (10 points)
Story progression in Act 1, Chapter 6.
Green as Grass (10 points)
Train the rook (any difficulty).
Guerilla Tactician (50 points)
Complete all campaign acts on Normal Difficulty.
Have Fun Storming the Castle (10 points)
Story progression in Act 4, Chapter 6.
Heartbroken (10 points)
Story progression in Act 2, Chapter 6.
Hoard the Horde (30 points)
Survive all 50 waves of Horde (any difficulty, any map).

It's a Trap! (10 points)
Story progression in Act 1, Chapter 2.
It's Good to be the King (10 points)
Win 10 rounds of Guardian as the leader (public).
Kick 'Em When They're Down (10 points)
Perform all 11 unique executions on a downed enemy.
Longitude and Attitude (10 points)
Story progression in Act 3, Chapter 3.
Once More, With Feeling (10 points)
Perform 30 perfect active reloads (any mode).
One-Night Stand (10 points)
Complete 1 chapter in co-op on any difficulty (Marcus or Dom).
Open Relationship (30 points)
Complete 10 chapters in co-op on any difficulty (Marcus or Dom).
Organ Grinder (10 points)
Kill 30 enemies with a cover mounted Mulcher (any mode).
Pack Rat (15 points)
Recover 20 collectibles (any difficulty).
Party Like It's 1999 (30 points)
Play 1999 rounds of multiplayer (any mode).
Photojournalist (10 points)
Submit a spectator photo.
Pound of Flesh (10 points)
Use a meatshield to save your life 10 times (any mode).
Said the Spider to the Fly (10 points)
Kill 10 enemies with a planted grenade (any mode).
Seriously 2.0 (50 points)
Kill 100,000 enemies (any mode).
Shock and Awe (10 points)
Kill 30 enemies with the heavy Mortar (any mode).
Smells Like Victory (10 points)
Kill 30 enemies with the Scorcher Flamethrower (any mode).
Standing Here, Beside Myself (10 points)
Win 3 matches of Wingman (public).
Suicide Missionary (150 points)
Complete all campaign acts on Insane Difficulty.
Takes a Licking (30 points)
Melee 30 Tickers (any mode).
Tanks for the Memories (10 points)
Story progression in Act 3, Chapter 4.
That Sinking Feeling (10 points)
Story progression in Act 2, Chapter 4.
There's a Time for Us (10 points)
Story progression in Act 4, Chapter 2.
Tourist of Duty (25 points)
Complete all campaign acts on Casual Difficulty.
Variety Is the Spice of Death (30 points)
Kill an enemy with every weapon in the game (any mode).
Water Sports (10 points)
Story progression in Act 3, Chapter 6.
You Are the Support, Son (10 points)
Story progression in Act 5, Chapter 2.
You Go Ahead, I'll Be Fine (10 points)
Win three matches of King of the Hill (public).