<Li> The Jockey: a male Infected that jumps onto a Survivor's back and steers them into other Infected or environmental hazards (e.g. Spitter goo), whilst clawing at the player's head until the player is incapacitated, killed, or shoved off . </Li> <P> As in the first game, an artificial intelligence system called the AI Director drives gameplay by procedurally spawning enemies, weapons and items based on players' performance during any given campaign . In Left 4 Dead 2, the Director has been improved to encourage more participation by players, forcing players through difficult gauntlets to reach safety . It also has the ability to alter elements of the level, such as placement of walls, level layout, lighting, and weather conditions, making each play session unique . The Director now rewards players for taking longer or more difficult paths through each episode by providing useful equipment, such as special ammo packs or higher tier weapons, along these riskier paths . </P> <P> 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 . </P> <P> Left 4 Dead 2 features a new cast of human Survivors, which include: Coach (voiced by Chad Coleman), a portly high - school football coach with a bad knee (although it does not affect gameplay); Nick (voiced by Hugh Dillon, motion capture by Adam Karst), a cold and sarcastic gambler and con artist; Rochelle (voiced by Rochelle Aytes), a low - level production assistant reporting on the evacuation for a local television station; and Ellis (voiced by Eric Ladin), a friendly (and rather talkative) mechanic who often talks about his friend Keith and their many misadventures . In addition to the four playable characters, Left 4 Dead 2 also features a supporting character in the form of Virgil (voiced by Randall Newsome), a Cajun boat captain, who appears (voice only) in the game's final three campaigns . </P>

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