Screenshot via Game Guides Pro Back 4 Blood is Turtle Rock Studios’ latest co-op zombie shooter, and it brings unique concepts to the table, including the Supply Lines system. Players must learn to use this system to earn the best items and buffs the game has to offer, a must for those trying to face the toughest encounters in Back 4 Blood. Supply Lines are where players spend earned Supply Points to purchase new cards for their decks and cosmetics for characters and weapons. Players earn supply points by playing Back 4 Blood missions and even get bonus points for completing levels. Players can access Supply Lines with the in-game menu through the Supply Lines tab. Related: How To Earn Supply Points In Back 4 Blood Supply Lines Each Have Their Purposes, So Read Each Supply Line Description Before Purchasing An Item. Players must also complete the supply lines in order from start to finish. Players cannot skip entries in the row. The higher the difficulty, the more supply points players can earn. Be warned that Veteran and Nightmare in Back 4 Blood are much less forgiving than Recruit. For more information on Back 4 Blood, see How to Ping Back 4 Blood Items on our guides.