Defibrillator

The defibrillator pack is one of the most interesting new items, but it also takes up the first-aid slot, making you unable to carry around a health pack as long as you have it. As its name says, it is the shock pad that doctors and paramedics use to revive people whose hearts have stopped. In-game, this translates to being able to resurrect dead teammates, as long as you know where their body is. This makes remembering where a teammate died incredibly important, as you can find a defib pack, run to the corpse, and pull it back. However, you generally do not want to carry these around, as the health kit is far more important. They are best used by running back to them, rather than carrying them at all times. Unless you have the free slot, that is.


Weapon Upgrades

Weapon upgrades takes up the first-aid slot, much like the defib pack. However, you will rarely have it in your inventory longer than a few seconds, as it is suggested that you deploy it immediately. There are three different possible weapon upgrades: explosive, incendiary, and laser sight. Explosive does a tiny but of extra damage any will cause every shot to explode when it hits. This is extremely effective against Special Infected, as it will consistently stagger everything except a tank. The incendiary rounds deal a lot more damage and set whatever they hit on fire, making them perfect for hordes and killing Tanks. Finally, the laser sight makes all weapons more accurate. This include the shotgun, where it tightens the spread on the pellets considerable.

Adrenaline Shot

The new item for the pills slot, it may not look like much. It only provides you with 30 temporary health and has a much bigger drug-like effect on you than the pills do. What you may not realize, however, is that the adrenaline shot also does two extra things. First, it makes you perform almost all actions twice as fast. This is perfect for pulling up downed survivors or bashing away Infected. The second effect is that you ignore slow-down from damage. Is there a horde blocking your path? No problem! Pop an adrenaline shot and run straight through. It's a lot more useful than the pills, but, like the defib pack, it is not something you want to carry around with you everywhere. The speed boost is incredibly useful in a tight spot, but pills allow you to survive longer overall. This is more of a person preference than the defib pack, however.

Boomer Bile

The new grenade, the Boomer Bile is just that: a vial of Boomer bile. It functions by attracting the undead to that particular location as though the Boomer had vomited there. It will also spawn new Infected if there are not enough to swarm, so it also acts as a mini-horde creator. While this sounds like a very bad thing to give to players, there are a few benefits. First of all, Infected will completely ignore all players as long as the bile is around. Then there's the fact that it will cover enemies in bile, which causes infected to attack them. It's most useful on Special Infected. This is especially hilarious on a Witch, as you can hit her with the bile and watch as a horde swarms her, making her unable to move as you simply walk by. The only Special Infected you don't want to hit with the bile is the Tank, as it doesn't really affect him at all.


Magnum

With the advent of melee weapons, one might think that there would be no pistols. That's dead wrong. While there are still the single and akimbo pistols, there is also a new weapons known as the Magnum. Resembling an Israeli Desert Eagle, the Magnum is an incredibly potent pistol that can not be dual-wielded and only has eight rounds in the clip. Every single round, though, has roughly the stopping power of a shotgun. A single round will down Common Infected no matter where you hit them, and three rounds are enough to kill most Special Infected. It's an incredibly potent weapons, but one must sacrifice the other pistols and melee weapons for it.

Melee Weapons

Melee weapons are all the rage in Left 4 Dead 2, as they are incredibly entertaining. As their name states, they are only usable in melee. Any and all melee weapons replace whatever you have in your pistol slot, which can reduce your ranged capability. Grabbing a melee weapon is always a major risk. However, if you are incapacitated, you will be able to use a pistol while downed and still retain your melee weapon while up. There are three categories of melee weapons. The first are blunt weapons, which include things such as the baseball bat or paddle. These deal less damage than the sharp weapons and, in general, are much weaker, at least in appearance. Next comes sharp weapons, which includes machetes and swords. These will effortlessly dismember enemies and are the weapon of choice for a melee user. In its own category is the chainsaw. An incredibly powerful melee weapon, the chainsaw can kill almost any Infected, Special included, in seconds flat. You can even kill a Witch without stratling it! However, the chainsaw has a limited gas tank and a slow start-up time along with being relatively rare.

AI Director Changes

The AI Director is now far more cunning, difficult, and interesting in general. You will almost never see less than three Special Infected at a time, and the AI Director will put them in places which harm you the most. The director never puts all of the advanced weapons in the same place anymore, instead spreaidng them out over the map and forcing players to scavenge and make decisions with actual consequences. The AI Director can also change paths through the level, although the basic path will always remain the same. It can even control the weather! The general gist is that Left 4 Dead 2's AI Director ratchets up the difficulty a lot, and we would have it no other way.