There are the five special infected enemies from the first Left 4 Dead, and then there are three additional members of the special infected, introduced here, in Left 4 Dead 2. The five special infected from the first game are the Boomer, Smoker, Hunter, Tank, and Witch. The three new special infected, introduced here, are the Spitter, Charger, and Jockey. Below is a brief description of each.
Just like in the first game, the boomer will move toward you, and attempt to puke on you, attracting the zombie horde to you. Shove them away from you, and shoot them, making sure none of your teammates are near it, when it dies.
The smoker will wrap its very long tongue around you, and pull you towards it, then claw at you, until you’re incapacitated or dead. Once it gets its tongue around you, you’ll have about a second to kill it. Otherwise, you’ll have to depend on your teammates to save you.
The hunter sneaks up on you and leaps at you, from great distances. Once it pins you, it will then claw you apart, unless your teammates shove it away, or kill it, saving you. It IS possible to shove it, or shoot it and kill it, as it leaps at you, but very difficult.
The tank, with its enormous strength, is capable of killing you, with one hit. If it smacks you with its arm, and you go flying off a cliff, then you’re dead, and you’ll have to start the area over. Sometimes, though, you and your teammates can kill it, with enough effort.
The witch, unlike the tank, will not attack you, unprovoked. If you can sneak around her, then I would highly recommend that you do so. If not, then try throwing a Molotov at her, backing away, and shooting, until she drops. That’s your best bet for killing her. If she touches you, then you’ll be incapacitated. After that, she’ll claw at you, until you’re dead, or your teammates kill her.
The Spitter is a female member of the special infected, who spits out wads of stomach acid that splatter at you, and will drain you of more and more of your health, the longer you’re in it. When she dies, she leaves a puddle behind, so be careful not to step in it.
The Charger will rush at you, attack you, and attempt to capture you and carry you away, with its huge arm, and knock you into the ground. If that happens to you, then you’ll be helpless, until one of your teammates comes along and either stuns or kills it. My recommendation would be to gang up on it and kill it, before it gets to you. Maybe throw a Molotov at it.
The Jockey will leap onto your back, and push you into a direction that you don’t want to go, leading you into harm’s way. Then, it will claw at you, until a teammate shoves it off or kills it.