Bonus multiplayer skins - Successfully complete the indicated task to unlock the corresponding skin in Multiplayer mode:

Anthony Carmine: Successfully complete Act 1 in the original Gears Of War.
Minh Young Kim: Find 10 COG tags in the original Gears Of War.
RAAM: Defeat RAAM in the original Gears Of War.

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Green as Grass (10 points): Train the rook (any difficulty).
It's a Trap! (10 points): Story progression in Act 1, Chapter 2.
Escort Service (10 points): Story progression in Act 1, Chapter 4.
Girl About Town (10 points): Story progression in Act 1, Chapter 6.
That Sinking Feeling (10 points): Story progression in Act 2, Chapter 4.
Freebaird! (10 points): Story progression in Act 2, Chapter 5.
Heartbroken (10 points): Story progression in Act 2, Chapter 6.
Longitude and Attitude (10 points): Story progression in Act 3, Chapter 3.
Tanks for the Memories (10 points): Story progression in Act 3, Chapter 4.
Water Sports (10 points): Story progression in Act 3, Chapter 6.
There's a Time for Us (10 points): Story progression in Act 4, Chapter 2.
Better Wrapped in Beacon (10 points): Story progression in Act 4, Chapter 3.
Have Fun Storming the Castle (10 points): Story progression in Act 4, Chapter 6.
And the Horse You Rode in On (10 points): Story progression in Act 5, Chapter 1.
You Are the Support, Son (10 points): Story progression in Act 5, Chapter 2.
Brumak Rodeo (10 points): Story progression in Act 5, Chapter 4.
Does This Look Infected to You? (10 points): Story progression in Act 5, Chapter 5.
Tourist of Duty (25 points): Complete all campaign acts on Casual Difficulty.
Guerilla Tactician (50 points): Complete all campaign acts on Normal Difficulty.
Artist of War (75 points): Complete all campaign acts on Hardcore Difficulty.
Suicide Missionary (150 points): Complete all campaign acts on Insane Difficulty.
Collector (5 points): Recover 5 collectibles (any difficulty).
Pack Rat (15 points): Recover 20 collectibles (any difficulty).
Completionist (30 points): Recover all 41 collectibles (any difficulty).
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).
Friends with Benefits (50 points): Complete all acts in co-op on any difficulty (Marcus or Dom).
Once More, With Feeling (10 points): Perform 30 perfect active reloads (any mode).
Takes a Licking (30 points): Melee 30 Tickers (any mode).
Organ Grinder (10 points): Kill 30 enemies with a cover mounted Mulcher (any mode).
Shock and Awe (10 points): Kill 30 enemies with the heavy Mortar (any mode).
Said the Spider to the Fly (10 points): Kill 10 enemies with a planted grenade (any mode).
Crowd Control (10 points): Melee 10 enemies down with the Boomshield equipped (any mode).
Smells Like Victory (10 points): Kill 30 enemies with the Scorcher Flamethrower (any mode).
Variety Is the Spice of Death (30 points): Kill an enemy with every weapon in the game (any mode).
Seriously 2.0 (50 points): Kill 100,000 enemies (any mode).
Standing Here, Beside Myself (10 points): Win 3 matches of Wingman (public).
Beat the Meatflag (10 points): Capture 10 meatflags in Submission (public).
It's Good to be the King (10 points): Win 10 rounds of Guardian as the leader (public).
You Go Ahead, I'll Be Fine (10 points): Win three matches of King of the Hill (public).
Back to Basic (10 points): Successfully complete the 5 lessons of multiplayer Training Grounds.
Party Like It's 1999 (30 points): Play 1999 rounds of multiplayer (any mode).
Around the World, Again (30 points): Win a multiplayer match on each map (any mode).
Dirty, Dirty Horde (20 points): Survive the first 10 waves of Horde (any difficulty, any map).
Hoard the Horde (30 points): Survive all 50 waves of Horde (any difficulty, any map).
Crossed Swords (10 points): Win 10 chainsaw duels (any mode).
A Parting Gift (20 points): Kill 10 enemies with a grenade while down but not out (any mode).
Pound of Flesh (10 points): Use a meatshield to save your life 10 times (any mode).
Photojournalist (10 points): Submit a spectator photo.
Kick 'Em When They're Down (10 points): Perform all 11 unique executions on a downed enemy.