The Developer Commentary is an extra mode in Left 4 Dead 2. In it, a player is able to listen to audio comments made by the developers, while they play through a campaign in the game with a significant lack of difficulty, as all Infected will ignore the player and only attack the AI Bot Survivors. The mode takes place in The Parish with icons called Commentary Nodes throughout a campaign, which trigger a specific audio comment when the player presses the "use" key while looking at the icon with your crosshair. Some Commentary Nodes, when activated, will spawn objects, characters, and even scripted events. Though there are enemies in the game, there are no Special Infected unless the player has spawned them by a node, and the Common Infected generally ignore the player unless the AI Survivors are all dead, in which case Common Infected will attack the player. No common infected will spawn in Crescendo Events or the finale. If all of the AI Bots are dead, spawned Special Infected will go idle. Due to this, no Achievements may be earned, but it is a way of practicing a number of skills.
Left 4 Dead 2 is a 2009 multiplayer survival horror game developed and published by Valve. The sequel to Turtle Rock Studios's Left 4 Dead, it was released for Windows and Xbox 360 in November 2009, Mac OS X in October 2010, and Linux in July 2013.
Left 4 Dead 2 builds upon cooperatively focused gameplay and Valve's proprietary Source engine, the same game engine used in the original Left 4 Dead. Set during the aftermath of an apocalyptic pandemic, Left 4 Dead 2 focuses on four new Survivors, fighting against hordes of zombies, known as the Infected, who develop severe psychosis and act extremely aggressive. The Survivors must fight their way through five campaigns, interspersed with safe houses that act as checkpoints, with the goal of escape at each campaign's finale. The gameplay is procedurally altered by the "AI Director 2.0", which monitors the players' performance and adjusts the scenario to provide a dynamic challenge. Other new features include new types of special infected and an arsenal of melee weapons.
Like its predecessor, Left 4 Dead 2 is set in the aftermath of a worldwide pandemic of an infectious disease known as the "Green Flu", which rapidly transforms humans into zombie-like creatures and mutated forms that demonstrate extreme aggression towards non-infected (much like the infected in 28 Days Later). Few humans are immune to the disease, still carrying the infection but showing no symptoms. The Civil Emergency and Defense Agency (CEDA) and the U.S. Military create safe zones to attempt to evacuate as many American survivors as possible. Left 4 Dead 2 introduces four new Survivors: Coach, Ellis, Nick, and Rochelle, who are immune to the disease and have individual back stories that are provided through character dialogue. While the game is intended as a continuation of the original, occurring one week after the first game begins, Valve decided to create a new group of Survivors due to the change in location. Like the first game, the five campaigns in Left 4 Dead 2 are set across a story arc, set in the Southern United States, which starts in Savannah, Georgia, and ends in New Orleans, Louisiana. The four Survivors have to fight their way through hordes of Infected, using safehouses along the way to rest and recuperate in order to reach extraction points.This "campaign" was set on The Parish campaign.
