Back 4 Blood Back 4 Blood is a thrilling cooperative first-person shooter from the creators of the critically acclaimed Left 4 Dead franchise. You are at the center of a war against the Ridden. These once-human hosts of a deadly parasite have turned into terrifying creatures bent on devouring what remains of civilization. With humanity’s extinction on the line, it’s up to you and your friends to take the fight to the enemy, eradicate the Ridden, and reclaim the world.