Gamestop's God of War: Ascension pre-order bonus is an exclusive multiplayer costume taken from Zack Snyder's 2007 movie 300, because nothing says "brand-new video game based on Greek pseudo-mythology" like a random costume from a five-year-old movie based on Greek pseudo-history.
Specifically, the costume replicates King Leonidas' red cape, helmet and "armor," which we assume is what they're calling his tiny little baby man-shorts. The costume also includes a spear that provides new moves and abilities, as well as a double-sided God of War: Ascension poster. It does not, however, include a pit for disposing of foreign dignitaries or a bottle of chest grease.