Borderlands 2. The codes will unlock Halloween-themed character customization skins, including the above buzzy little number for Maya.
The giveaway kicks offs at 11AM ET (8AM Pacific, 3PM British) on Gearbox's Twitter and Borderlands' Facebook pages, and codes will be active until November 5 at 0.55AM ET. For extra fun, dress up like the skin you win when you go Halloween-ing tonight. Even though people won't get it, you'll definitely look super cool*.
*Joystiq offers no guarantee of your cosmetic coolness