Left 4 Dead 2: The Passing (PC)

On December 14, 2009, Valve announced the first DLC installment for Left 4 Dead 2, "The Passing". Though initially planned to be released sometime in March 2010, "The Passing" was released on April 22, 2010. The content costs 560 Microsoft Points for the Xbox 360 and is free for PC users.
The campaign, taking place between the "Dead Center" and "Dark Carnival" campaigns, features the cast of Left 4 Dead 2 meeting with three of the survivors from the original Left 4 Dead. The new group learns that the 4th Left 4 Dead survivor, Bill, sacrificed himself to allow his comrades to continue on safely; the title "The Passing" is in reference to Bill's sacrifice. A campaign for Left 4 Dead will be released sometime after "The Passing" as a prequel to the events describing Bill's sacrifice "The Passing" contains a reference to Frank West and Otis, characters from Capcom's zombie-themed game, Dead Rising.
The campaign is a three-map campaign, unlike the "Crash Course" campaign for Left 4 Dead which was only two maps. The campaign introduces a new uncommon infected in the form of the 'Fallen Survivor', a well-equipped zombie that may drop items the players can use, however for balancing reasons it will actually try to run away rather than fight, making the valuable items it carries harder to attain. The add-on also features new weapons, an M60 machine gun which becomes unusable once depleted of ammo, and a golf club for melee. New game modes, "Mutations", are offered every week after "The Passing"'s release; these game modes alter the conditions of play, such as "Realism Versus" mode or "Chainsaw Massacre" where each player is given a chainsaw with unlimited fuel.