I have unistalled the game, so I will not be able to put videos up. If you want to see videos on this guide, sumbit your own and I will add them to it.

This guide is going to cover pretty much everything. Did I miss something? Let me know and I will add it.

Hello, people call me Panda but in-game I'm Mr. PandaBear™. People in this community don't like me for some reasons but the ones I deduce is that because I speed run through maps and I have a different play style than them. I'm a retired L4D versus player, I still play versus but just with friends in the competitive scene, I play some pub versus, but now I mostly play pub campaigns. I am also an eight year veteran of this game, meaning I have been playing since Turtle Rock release in 2006 or if you only care about Valve then I am a 6 year veteran, so I know what I am talkng about. I also play with 10-15 fps so I'm sure you can do better than me.

Campaign
I recommend playing this first to learn the feel of the game, Play Easy-Advanced if you are learning, Some kids in Expert are try-hards and care about everything you do and will kick you because you don't listen to them. If you're going to play Easy then expect to never die and get the easiest kills of you life. Same with normal unless your team doesn't clear you when you're pinned by a hunter or smoker. Maybe even by a witch if they don't shoot when you miss the crown or accidently startle her.
Versus
The pros domain. Versus is like campaign but you get to play as the infected while the other 4 people are against you. Your job as the infected is to down/kill every survivor before they reach the safe room you take turns every chapter so you play each chapter twice. To win in versus you must have the most points.
Survival
Lol no one plays this anymore. Some people do play this but only in private games. the goal is to survive as long as you can from Common infected and Special infected.

There are a total of six campaigns or seven if you include the one in survival
The campagins are called:
No Mercy
This takes place in Fairfield and the survivors head towards a hospital for evac. from a passing helicopter. You make your way through Apartments, The Subway Station, Sewer, Mercy Hospital, and the Rooftop Finale
Crash Course
This takes place after Farfield when the evac chopper from Mercy Hospital crashes near the Turnpike in Death Toll. You crash because Zoey shot the pilot. You start from the alleys to the garage to find the armored truck to escape
Death Toll
This resides in Riverside after your path is blocked you head down the tunnel to the Drainage system then towards the church then into the town and end up in the Boathouse Finale
Dead Air
You're in a greenhouse thats bigger than my house. After you see a convient plane fly above you. You head to the airport by going across the Rooftops to a Construction Site, then an Airport Terminal then you're on the Runway Finale.
Blood Harvest
Congrats you're now lost in a forest forcing you to follow a path leading to a Repair Warehouse then past a Bridge to a Train Station and being stuck at the Farmhouse Finale, to be rescued by a armored car.
The Sacrifice
After the whole comic thing in Left 4 Dead you arrive to a Shipyard by train. After pushing off the hordes you fight a imprisoned tank inside a train car then climb up some rocks where birds ensure your deaths then raising a bridge to safety then a generator breaks dajavu then a Survivor must sacrifice himself (Storyline is Bill Sacrifices himself)
The Last Stand (Survival only)
You find yourself at a lighthouse and survive then die horribly because you missed that one bullet. Because Survival.

Every game you start you will spawn with one Pistol, but you always spawn in right next to a counter or table with guns.
In early chapters you will start with on the table is a SMG and a Pump Shotgun

SMG
Has a carrying capacity of 480
A clip size of 50
The damage per shot is 20
If you can get every bullet in your clip into an enemy you will do 1000 damage this can decimate a tank, an SMG is a decent weapon does alright damage to enemies and is extremely good if you can aim and control the spread.

Pump Shotgun
Has a carrying capacity of 128
A clip size of 8
Does 240 damage if you get all the pellets in your target (24 damage per pellet)
If you get all 8 shots plus all the pellets in your target you will do 1,920 damage
This gun is my all time favorite due to its speed and reliability I would trust this gun more than the Auto Shotgun

Tier Two
Assault Rifle
Has a carrying capacity of 360
A clip size of 50
It does 33 damage per shot with a total of 1650 if you get all 50 shots in your target
This gun is great if you can aim and control the spread on it.

Auto Shotgun
Has a carrying capacity of 128
With a clip size of 10
does 286 damage if all pellets hit the target (Contains 11 pellets in one shot each pellet does 26 damage each)
Has a rate of fire of 200/minute
Does a total of 2860 damage per clip, A lot of people prefer this gun, but spamming it is just hilarious. Countless of people in games waste 4-7 shots on one CI even though it takes one shot.

Hunting Rifle
Has a carrying capacity of 150
A clip size of 15
It does 90 damage per shot
With a full clip damage of 1350
This is my all time favorite T2 one shot kills on headshots, can stumble witchs, chip tanks to death, clear CI from afar.

Pistols (This is a T1 weapon)
The carrying capacity on this gun is infinite so fire away
The clip size for one pistol is 15 and if you dual wield its 30.
Damage per shot is 35
If you get all 15 shots in a target you deal 175 damage and all 30 is 350 damage.
Excellent guns to use against a tank to slowly decimate him, this gun on campaign against a tank can make you invincible.

Pipe Bombs
This throwable is a one time use until you find another throwable
Pipe bombs are a nice way to clear hordes and also to get them off you if you are getting overwhelmed.
These are explosion based throwables which haves a blast radius of 3-4 meters
This can kill as many as 20 CI in the radius and do some deadly damage if you are close to the explosion which will also stumble you.

Molotov
This is also a one time use throwable.
When you throw a molotov if will last to 15-17 seconds long
The fire spreads a bit before it goes out so make sure you have some distance from it.

When you use a throwable it can set off propane tanks, gas cans and oxygen tanks.

These guys are stranglers on your way to the safe room and come in hordes every certain amount of time (it changes a lot) hordes also come in if you get boomed on by a Boomer or start a crescendo event.
The health on these fellas are:
Easy-30
Normal-50
Advanced-50
Expert-90
Max hits are:
Easy-2
Normal-3
Advanced-5
Expert-20
Also if the CI hit you form behind they deal half the damage so:
Easy-1
Normal-2
Advanced-3
Expert-10
The CI are your worst enemies imo because I see more people wipe from them more than anything mostly because they just shove them away and walk away. Shoving a CI isn't going to kill him unless you do it a lot to that CI. They slow you each hit and can grapple you in place.
People don't find these guys as much as a threat but they can ruin your aim, keep you place making you immobile. Clear these guys off your team but make sure you don't shoot your teammates because you will either hurt your friend more than the CI will or you make him worry about his back while infected come from ahead of him thus making him surrounded.
During hordes best place to go is in a corner so they can come at you at one direction, You can also move them to your liking they will follow a path to get to you and if you run back while lining them up you can kill more than 5 in one shot.
Pipe bombs are a nice way to get them off you guys since they will go attack the pipe bomb. When they start to spawn you can throw a molotov where they are spawning from to get rid of them faster.

The Boomer
The Boomer is the fat guy who vomits on you. He can get you to wipe fast if you can't clear the CI on you. He makes loud burping sounds and gurgling noises which changes to a lound groan if he sees a survivor
He has 50 hp which makes him very easy to kill
The Boomer also vomits bile on you which attracts a horde to attack you and any other survivor who he biled on.
When you kill a boomer in anyway he will EXPLODE and if you are near his radius you will get covered in bile and alert the horde.

The Smoker
The Smoker is a tall skinny guy with an acne problem on his face, while having his tongue sticking out.
He has 250 hp which will take some shots.
To hear him out he makes some high-pitched rasping and coughing.
A smoker can pull you away from your teammates and keep ensnarled by him or if someone or something is blocking your path he will keep you there while damaging you.

The Hunter
The hunter is hooded guy with some brown sweatpants with a bit of a hunch
He also has 250 hp
The hunter can leap off the ground when crouched and can pin survivors down and stumble others if near the one he pounced.
Hunters make a distinctive growl or a scream when he sees you and while he pounces and the snarls he emits when he spots you.

The Tank
The tank is the big hulking looking guy, has his own songy song to distinguish when he spots and attacks you.
He has various health on each difficulty
On easy he has 3000 hp. Fairly easy to kill
On Normal he has 4000 hp. Also easy to kill.
On Advanced he has 8000 hp. Takes a bit to bring him down
On Expert he also has 8000 hp. Takes a bit to bring him down.
The Tank can either Punch or Throw a rock at you.
The Tank can wipe a team at ease if the team doesn't work together. He can deal different amounts of damage nor can I remember how much he does on Easy, Normal, Advanced. Although on expert he can down you in one hit and kill you while incap'd in 2 hits.
The tank spawns in usually when players are doing well or just randomly, sometimes 2 tanks will spawn in a chapter.
Players always light the Tank with a molotov or a gas can which will buff his speed making him move faster. Not a great idea to do if you can't juke or out run the tank. Also a tank can outrun you if you are healthy (hp>39). I recommend you don't light the tank, people think it kills him fast although that is true because he has a burnout of 180 seconds. I recommend sharing aggro with the tank (aggro is who he is targeting) Me and my friends share aggro forcing him to change targets and not being able to down his initial target.
Do me a huge favor when you fight a tank, don't light him when a person is 5 feet away from it, because you will just kill your teammate. Don't RUN away from the tank and never shoot at it because its not going to die by itself.

The Witch
The Witch is the girl crying and sitting down while moving her head up and down slowly.
She is easily avoidable but sometimes she will spawn in your path.
To kill her you can throw a molotov or light her and run away, unlike the tank she gets rather slower and will burnout in around 12 seconds. You can also Crown the witch, meaning you kill her in ONE SHOT/head shot not spamming your auto shotgun at her.
Also if you get in the way of the Witch when she chases the person who startled her, she will change her target to you.
On Easy and Normal a witch can be crowned in the body but on Advanced and Expert you must shoot her in the head. On Advance and Expert the Witch has shotgun resistance on Adv she has 35% on her body and 70% on expert.
Also more ways to kill her which I will provide videos for.

Crowning a Witch on Easy requires you to shoot her in the body or head. It takes one shot to kill her with a Pump Shotgun or Auto Shotgun.
On Normal it is the same as Easy, one shot will kill her.
Once you are on Advanced a body shot will not kill her in one hit, it will take two. A headshot is required to kill her in one shot.
Expert is the same as Advanced. Body shots will take two shots. Headshots only needs one shot.
If you miss the witch on Easy-Advanced, she will down you. On Expert if you miss and she hits you, you are instantly dead.

You just need a pistol and a shotgun for this to work. Get a nice distance from the witch and mow her down with your pistol(s) and soon as shes getting to you pull out your shotgun and shoot her at point blank.

Get some distance from her, that you think is enough to put 15 bullets in her.
Headshotting her while shes crying will stumble her (you can run up and shove her and continue the stumble) And continuing to shoot her will kill her, you do not need to reload your rifle for her to die.
Your team can help also will bring her down faster.

Weapons being used are the Propane tank, Oxygen tank, and Gas can.
If a Witch is set up by any enviromental fire or something that will cause the tanks or cans to set off by the word, will have the Witch have no target and stumble away, this is usually by the Gas can, she wil sometimes attack you from the propane or oxygen going off.
When she get stumbled from the explosion you can melee her which will extend her stumble.
If she gets lit from the gas can, just let her burn or if she isnt in the fire anymore you can shoot her to bring her down faster.
If a witch hits the Tanks or Can and destroys them, she will stumble or burn herself.
Using a door is perfect for this, she will have to break the down while also hitting the tank or can you placed there
The placement of it has to be on the side where she is, not where you are.

When you get pulled in a campaign game, the Smoker's hitbox will mostly show his head infront of him which allows you to headshot him with one shot.
The farther he is, the better your aim will have to be.
An achievement is given when you do this, it is called Tongue Twister.
In the video I am in versus, but the smokers are bots and will die easier than a Player controlled Smoker, since they have different hitboxes

Deadstopping means to shove a hunter while hes in mid-air. This is used to prevent a hunter from either pouncing you or your friend.
When you deadstop a hunter, he will begin to stumble and he can still scratch you. Kill him fast or back up a bit.

Skeeting is shooting something in mid-air. In Left 4 Dead this applies for a Tank's rock, a hunter, or a dive bombing boomer.
When a tank throws a rock, you can skeet it as it flys towards you. This destroys the rock.
You can't skeet a rock as it leaves his hands, the rock has a couple of god frames. Let it travel about half the distance.
IN the video you may notice the red lines that follow the tank's rock. This is a console command that requires sv_cheats on. It debugs the rock to show its path and hitbox.

Slowing down a tank requires an automatic weapon. Dual pistols, Smg, Assault Rifles. Auto shotgun will slow him, but he will catch up.
This tactic is good for kiting a tank so he is unable to hit you. You can use this with him having to climb over an obstacle like a fence, truck, unpunchable prop etc. this will force him to stop and climb and slow down even more giving you time to reload or pop some pills.

In versus mode SI will have different Hitboxes and maybe easier or hardr to kill depending on their skill levels.
SI in Versus still have their same abilities they will just attack as a team and there can be four specials alive instead of three.
Just be sure to clear your team when they decide to attack you.

The same as campaign, except when the game starts becoming late more and more will spawn faster
Just stick close and clear your team.

Versus can be competitive to some people and just for fun. If you just want to play for fun then play a game with friends rather than joining a pub.
Now when you're playing versus always stick by your team and call out SI, it'll help you stay alive and let your team know where a specific SI is. Calling them out could possibly save your team from a quad cap or just from getting pushed back.
Quads are when all SI can pin you down leaving you immobile. Lets say theres 3 Hunters and 1 Smoker, that is a quad. When the team has a quad they will attack fast and hopefully in a coordinated manner. I recommend getting rid of their quad.. The Smoker will possibly attack first then the Hunters jump in to cover the Smoker. You can try to save the smoked friendly but also keep in mind that there is 3 Hunters coming in so look around or if you have an HR snipe the smoker.
Now if you're the infected team and you have a Quad, let your team know your ready by teamsaying "r" or "ready" or just VC it. Attack in a coordinated manner don't just jump in praying. If you're the smoker and they just have one carry (someone who is doing all the work to keep their team alive) then smoke him so he can't be the one skeeting the hunters when they come in. If you're the Hunter and the carry got smoked. Be fast enough to cover the smoker so the person smoked doesn't get free.
The most important thing to do is to stay by your team at all times if SI are down you have 20-ish seconds to wander or push foward. I mostly shop/look for items when SI are down or if you play survivor second, you can free spectate to look for items. You will most likely get the same item spawns.
Save molotovs for tanks if you know one is coming, if you light a tank it will force him to nearby water if any is available so he can be unlit. If there is no water it will force him to play aggressively.
If you get tank and you know you're gonna fail with it, pass it, To pass don't attack anyone and just hide you're rage meter will go down and give it to another player on your team. You can only pass once before the tank goes AI.
Don't be all aggressive with the tank because they will gun you down, wait for support by your fellow SI. you can go to a vantage point and throw rocks, most skilled players will skeet the rocks or just dodge them.
Use cars and dumpsters or any other punchable prop, but dont just use those because you will be an easy target. Throw a rock and maybe if you hit someone you can hit the prop to them and down them. If survivors are to far for a hit kill the downed survivor with the prop. Why? Because they lose points if they make it to the safe room.
If you're against the tank stay by your team but in a seperated manner so he can't down all 4 of you with one prop. Don't strand so far though because his support might get you and forc your team to go help you, losing focus on the tank who will jump in to kill you.
Skeet the tanks rocks if he just throws them, avoid the props he hits to you because they will incap you in one hit. Hear a boomer or smoker? Let your team know so you don't get boomed or pulled away because if you get boomed on or pulled the tank will tank advantage of that and possibly wipe your team.
Now if a Witch is nearby make sure SI is down before you go ahead and tyr to crown her because you will get smoked or boomed or hunted right before you crown her. Some SI will scratch her while you walk up to forcing her to get up faster and attack the first person in her sight.
Also attack in teams. Don't just attack one by one unless you spawn very fast. If there is 4 players on your team your spawn timer will be above 20 seconds. If you attack with all 4 you can possibly hurt the team and force them to waste kits.
Which brings another nice point, don't waste kits like theres no tomorrow because they give you points (Health Bonus). Pills don't help this bonus.

When a Friend is down
Clear him first before you start picking him up, please.
When an ally is down you want to focus on him taking the least amount of damage because you take somewhat more damage when downed. Besides when he is down and takes damage except from fire, he is knocked back down, and the meter where you're picking him up is almost done and he gets hit from a CI he is knocked back down and you have to restart that meter.
Be a gent. Clear first.
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As Tom stated above. Make sure you AIM a bit HIGHER than where your friend is, it will help by you not killing me instead of CI. Because we all know aiming is hard *cough* *cough*

If a friend has been boomed on
Sure you're friend is blind, so clear him, just dont shoot him because who are you really helping. I can personally see through bile after hours of training.... thanks jessi and I can clear myself at ease but a lot of people can't see through bile and will need help clearing so give em a hand, just don't blow off theirs

If a friend is pinned, smoked
Help them ASAP because one they're dying, two they live longer hopefully
If a friend gets pinned by a hunter or smoked by a smoker he can't help you, so if a Tank is attacking you guys and a friend or two gets pinned and smoked, change your Priority to them they can help you down the tank faster.

How to call out SI
1)Open your eyes
2) Spot an SI
3) Tell your team where he's at so they know
4)Die from SI for the lols
5)profit!?

How to play Expert
This isn't hard to play it's rather easy.
1) Learn to not shoot teammates because of obvious reasons
2) Clear CI don't shove and walk away
3)Rage quit because you died and will never respawn then join a new expert and spawn in dead and Rage quit again because you have problems.

How to clear
Kill CI, kill some more CI, kill even more CI... Did I mention to kill CI?
Kill some SI wait about a minute or less... kill SI again.

Medkits
I'm a versus player, I don't waste these unless it is nescessary (I'm b/w, tank incoming, find a kit, or in safe room.) Sure you can heal teammates people have it in their head that healing will cause more item spawns, this isn't really true because never seen it happened. They still spawned randomly.. healing teammates gives them the same health as if they healed themselves so don't argue that it heals them more. And for the love of god don't heal someone when theres a horde or a tank 10 feet away. Why? because its illogical

Pills
These stuff of stuffs give you degrading health which goes out in time. Don't heal when someone takes pills because you just wasted his pills. plus pills spawn more than kits unless you're doing terrible and the director feels bad for you all and spawns kits instead. So be a pal and pop pills like theres no tomorrow.

Be a teamplayer
Help your team! Stay by them! Help them clear!
Lets have a buddy system, if you're an ass to your team, they will most likely not help you. But if you are nice and are buddies during the game you will have each others back. I use to have a buddy in L4D named Tom we had each others back. We went out of our way to pull tanks off each other to always clear each other etc.
Get a buddy on L4D have fun and keep each other alive.
Staying close to your brochachos can ensure your safety and not having to worry "Oh no I'm alone and will get killed by an SI" but not today! Because BUDDIES will save you!

When fighting a tank
Make sure you clear the area of CI and SI you want to fight the tank at.
Don't light the tank when someone is near him because it will result in that friends death.
Use the mini gun to draw aggro to you! this can save a downed teammate or pull aggro for aggro sharing.
Pull a tank off a down ally, you can do this by getting next to the tank and shooting and shoving him he will then target you but make sure you're close enough where he will chase you. He will atleast hit your downed friend once before chasing you
You can use obstacles to fight a tank to slow him down and to make him slower while also making him easier to shoot at.
You can use obstacles to make a tank have to climb a million times before he can't reach you because you just jump back and forth.. thats boring and requires no skill. So be a good and fight him where he has a chance to make it more interesting.
Use pistols or automatic weapons to slow him down, tank getting too close? spray at him with an automatic weapon to slow down his speed (he has to be running in your direction.)
Use propane to stumble the tank, this can make him stop throwing that rock or stop chasing you for a few seconds. be wary that shooting a propane tank close will stumble you and the tank will recover faster than you probably and you take damage from the explosion.
Skeet his rocks when he is afar, yes rocks are skeetable by any weapon. Don't try to skeet a rock as soon as he throws it, because it has god frames I'm not sure how many but it does. Give it some air time then shoot it.
Try dodging his rocks, use walls and other stuff (not teammates) to take the rock the tank tracks you when he is going to throw it and will hit you you can make him track you in one direction then strafe the other to dodge it. Simple right?

Fighting a Boomer
Don't shoot him when he's close to you.
Kill him before he pukes on your team.
Easy peezy lemon squeezy.

Fighting a Smoker
get near a wall or something to block his tongue and when he tries to smoke you go behind that wall. or if you're close enough you can tongue twist him (achievement for this) you kill him when he grabs you, he can die in one shot from a shotgun and few from a AR or SMG.

Fighting a Hunter
Change your path when he pounces he'll miss
Deadstop him then kill him
Be like people and just shove him because you have so much skill when it can take one bullet to kill him.

Fighting a Witch
Crown her with a shotgun and don't miss.
Ignite her and run. Don't get stuck on that desk.
Stumble her with an HR and shoot her death while she runs to you.
Avoid her.

Fighting against CI
Shoot them. Shove if they get close, then shoot them.
Horde? get to a corner then shoot them.
Throw a pipe then shoot the remaining CI
throw a molly at their spawn, shoot the ones that didnt burn.