There are three ways to unlock weapon skins in back for blood. The first way is through playing the game and earning experience points, levelling up your characters level will grant you a chance at getting a free weapon skin. The second option is by exchanging 3 diamonds for one of any rarity or more rarer weapons with no limit on how many you can buy. Lastly, if this isnt enough time sink to satisfy your need for increasing levels of customization, there is also an opportunity where players who have participated in tournaments during the week get DOUBLE XP every day after being DOUBLED out at 4pm PST!