In Gears of War 3 for the Xbox 360, you can unlock the Golden Retro Lancer as a weapon skin to use in the game.
The Golden Retro Lancer can only be unlocked if you played during the Gears of War 3 beta, getting 100 kills with the Golden Retro Lancer.
Check out my other guide for more unlockable weapon skins in Gears of War 3.
