Left 4 Dead

Left 4 Dead, or L4D, is a video game series exclusive to the Xbox 360 console and PCs. The storyline of each game follows four people (the Survivors) as they attempt to fight their way through waves of zombies (called Infected). Several types of Infected have special abilities in order to make them a greater challenge for the players. The first game was released in 2008 to predominantly positive reviews. The sequel, which included four new Survivors and three new types of Special Infected, came out a year later.

Gameplay usually involves teaming up with three other players in order to get through one of the specific campaigns. There is also a versus mode, where players are both Survivors and Special Infected.

The Infected
There are two major categories of Infected: common and Special. Common Infected are analogous to traditional movie zombies in their appearance, but have the running speed of more modern zombie interpretations. They band together in groups known as Hordes, which are drawn to loud or high-pitched noises. The second game introduced Uncommon Infected, which are essentially common Infected with some sort of special ability. Infected clowns, for example, will draw common Infected due to their squeaking shoes. There are eight different types of Special Infected, seven of which are playable in multiplayer verses mode. Agents operating in this continuum will often disguise themselves as one of these creatures. In alphabetical order, they are:
 * The Boomer, a morbidly obese Infected that vomits bile onto Survivors. The bile obscures their vision and attracts ordinary Infected. When killed, Boomers explode and cover any Survivors near them with more bile.
 * The Charger (introduced in Left 4 Dead 2) is a large and fast Infected that picks up Survivors with an oversized arm and runs off with them until it hits a wall or other surface. It then proceeds to smash the Survivor against the ground. Skilled Survivors can take advantage of this and trick Chargers into attacking; the Survivor is then able to get out of the way and the Charger keeps going until it crashes into a wall or falls off a cliff.
 * The Hunter, an Infected in a hooded sweatshirt who leaps onto Survivors and rakes them with his claws. Hunters are extremely quick and capable of jumping great distances, but give away their positions by emitting a loud shriek when they leap through the air and onto their intended victim.
 * The Jockey (introduced in Left 4 Dead 2), a hunchbacked Infected, can jump onto the backs of Survivors and steer them away from their friends into hazards or towards other Special Infected.
 * The Smoker, an Infected who can constrict and strangle Survivors with its prehensile tongue. They are called 'Smokers' due to their coughing and their ability to give off a field of obscuring smoke when killed. In the sequel their appearance has become particularly gruesome, with no less than six different tongues on their body, including the prehensile tongue. One of these tongues extends out of the back of its head.
 * The Spitter (introduced in Left 4 Dead 2) is a female Special Infected with a spitting power similar to the Boomer. Instead of bile, however, Spitters emit acid that can damage Survivors who accidentally stand in it. Her lower face and jaw are melted as a demonstration of how powerful the acid is.
 * The Tank is best described as an 8-foot tall undead version of the Incredible Hulk, with the ability to send Survivors flying with a single punch. Tanks are also capable of tearing chunks of concrete from the ground and hurling them at Survivors out of arms reach and can also punch larger objects to send them flying, crushing any Survivor that doesn't get out of the way. Their muscular build acts as a natural armor that renders bullets virtually useless, so Survivors must cooperate to kill a rampaging Tank and live to tell the tale. His arrival in the game is always punctuated by a dramatic music cue.
 * The Witch is a female Special Infected, and the only one to not be controlled by players. Her appearance is that of an emaciated girl in her underwear with white hair, long claws, and red eyes. Her appearance will be punctuated by the sounds of her sobbing. She will be found sitting on the ground, hiding her face and crying. Although she is initially nonagressive, she can be startled by a flashlight or loud noises; if this occurs, she becomes enraged and will attack the Survivor who startled her with surprising force. Quiet and careful Survivors may be able to sneak past the Witch without getting her attention.

Left 4 Dead and the PPC
Fanfiction about Left 4 Dead is often split between Mary Sue/Marty Stu survivors (or sometimes infected) and slash. Any L4D slash is typically between Survivors (Nick/Ellis from L4D2 being very popular), but there is also a great deal of femslash between Zoey from the original L4D and the Witch.

There are currently no known PPC agents originating from the Left 4 Dead continuum.

Missions in this Continuum
Agents Laura Dukes and Danny Richardson (DMS - Video Games)
 * Mission 002 - Dead Weight
 * Mission 003 - With A Side Of Chips And A Drink
 * Mission 004 - Night Of The Living Stu