Left 4 dead Perks
Anti Tank Unit: +15% Damage to The Tank
Unlock: Inflict 120,000 damage to Tanks and acquire either the Tankbusters or Man Vs Tank achievement.
Heavy Hitter: Larger punch reach and cone, double punch damage and increased chance of knockdown. Increased chance of hitting hunters out of the air.
Unlock: Punch 250 common or special infected to death and acquire any two of the following achievements: Dead Stop, Hunter Punter, Clean Kill, Spinal Tap.
Head-Hunter: +25% Damage to Headshots on any infected, and a +5% damage to Hunters
Unlock: Kill 5 Hunters with a headshot and acquire either the Jump Shot or the Brain Salad achievement.
Light Step: If you walk slowly, the aggro area of idle infected and the Witch becomes much smaller for you
Unlock: Kill less than 1000 infected through-out an entire campaign
Witch Hugger: Gives you the option to hug the witch by meleeing her, resulting in a 50% chance that she attacks you instantly, a 20% chance that she becomes un-aggroable unless physically attacked, a 15% chance that she runs away or a 5% chance that she joins the survivors and aids them in combat (a bonus is awarded on Verses mode if she survives to the end of the level.)
Unlock: Acquire the Do Not Disturb Achievement
Neo-Warrior: +15% damage with pistol weapons, -20% reload time on duel pistols
Unlock: Inflict 100,000 damage with pistols or Acquire the Akimbo Assassin Achievement
Blue Blood: Double Damage to common infected
Unlock: Acquire the Zombie Genocidest Achievement
Field Medic: -30% healing time on self and other players
Unlock: Acquire the Field Medic and Dead Giveaway achievements
Drug Dealer: Allows you to carry two pill bottles at once
Unlock: Acquire the Pharm Assist and Helping Hand Achievements.
Deep Pockets: +50% ammo for primary weapons
Pyrotechnitian: -50% damage for fire, larger area of fire from Molotovs and petrol canisters. Allows you to carry two Molotovs or use your grenade slot to carry a petrol canister
Unlock: Acquire all of the following achievements: 101 cremations, Burn the witch, Towering Inferno.
Demolition Expert: -50% damage from explosives, larger explosion radius from propane and gas canisters. Allows you to carry two pipe bombs at once or use your grenade slot to carry a propane or gas canister
Unlock: Acquire the Pyrotechnitian achievement and kill 250 infected with pipe-bombs
Monster Killer: +15% damage to all Special and Boss infected
Unlock: Achieve either Nothing Special, or all of the following achievements: Dead Stop, Drag and Drop, Cr0wned, Blind Luck, Hunter Punter, Tongue Twister No Smoking Section Man Vs Tank, TankBusters, Witch Hunter, Ground Cover, Clean Kill, Jump Shot.
Butcher: +5% damage to common infected, as well as a massively increased chance to gib them, and even disintegrate them with firearms
Unlock: Blow limbs off 150 common infected and acquire the Brain Salad achievement.
Fender: -25% less damage from being grappled by smokers or hunters
Unlock: Survive being incapacitated 10 hunters and 10 smokers
Duellist: Allows you to duel wield the SMG or the Pump Shotgun
Unlock: Acquire the Neo-Warrior Perk and inflict 1000 damage with duel pistols while you have that perk active. This perk can only be used if you have the Neo-Warrior perk active.
Kerb-Stomp: Punching infected who are lying or sitting on the floor kills them instantly
Unlock: Acquire the Spinal Tap achievement
Weapon Specialist-Shotgun: +20% damage from shotguns weapons
Weapon Specialist-Rapid Fire: +20% damage from rapid fire weapons (excluding the minigun)
Sniper: +20% damage from the sniper rifle, dramatically increased accuracy from all weapons when crouched or standing still, allows you to iron sight any primary weapon (using the sniper rifles zoom in control
Veteran: +10% damage using any weapon
Unlock: Survive all 4 campaigns on any difficulty
Ard-Man: +25 base health
Determination: While incapped, you get no accuracy or firing speed deprecation and you cannot die from bleeding out ; you have to be physically beaten, even if you only have 1 health while on the floor.
Unlock: Acquire the Ground Cover and Stand Tall achievements.
Infamous Bastard: 5% chance that zombies will flee in terror on seeing you for the first time (not applicable to horde or special infected)
Heavy gunner: Increased view on the minigun and instant death on any common or special infected while using the minigun (except the Tank and the Witch.)
Unlock: Acquire the Red Mist achievement
Strong Back: Allows you to Remove the minigun from its post and wield it as a weapon, but you automatically drop it the moment it overheats or you take damage (it can be picked up again.) Decreases your punching speed by half and movement speed to walking pace while carrying it.
Unlock: Acquire the Heavy gunner Perk, and kill 2000 infected with the minigun while that perk is active
Underdog: +50% damage from all weapons while your health is below 40
Unlock: Acquire the Dead Giveaway achievement and kill 1000 infected while your health is below 40
Optician: +50% visibility through smoker smoke and boomer bile
Unlock: Acquire the Blind Luck achievement.
Brain-dead: -50% stunning time from survivor punches
Unlock: Acquire either the Chain Smoker, or the Double Jump achievement.
Talon-Ho: +50% damage from meleeing survivors (+10% for the Tank)
Pack of lies: -50% damage taken from any source and +25% damage inflicted against survivors if another special or boss infected is close by (does not stack if there are more than one)
Unlock: As a member of a victorious team of infected, Kill all four survivors while in sight of each other
Stop-Drop: Fire only lasts for 5 seconds, rather than burning you to death automatically (Unless a hunter pounces on a survivor.)
Hate-Monger: +10 health every time you melee a survivor or idle common infected, +50 for killing a common infected, + 100 health for killing a survivor (+500 for the tank) and +50 health while pinning a survivor
Unlock: Kill 8 survivors outright as any special infected and acquire the Dead Wreckening achievement
Durability Issues: +50 Health
Stay Down: Double Damage to incapacitated survivors
Unlock: Inflict 2500 damage to incapacitated survivors and acquire the Lamb 2 Slaughter achievement
Barger: Leaping next to a survivor, even if you miss them, knocks the back
Unlock: Knockback survivors 20 times while leaping on another survivor
Trick Jumper: Double the distance you can wall jump and if you land on a wall, you stick to it, making wall jumping easier
Unlock: Acquire the Double Jump achievement
Ravager: Double the speed of your leap, and remove the limit of damage you can inflict from long jumping
Unlock: Inflict 25 damage from an initial impact while leaping
Silent Stalker: You make no noise while you crouch unless survivors are in your actual sight
Second Thoughts: Allows you to leap from pinned survivors to escape oncoming fire
Unlock: Survive being pushed off a survivor for ten seconds
Venomous Fog: Your smoke cloud does periodic damage to survivors as if it was a pool of fire
Volatile Chambers: The smoke cloud you create will explode if ignited or if guns are fired while inside it or near it. +50% damage from fire, and if ignited, you explode violently on death
Durable Tongue: Ensnared survivors take two hits to free them instead of one, -15% recharge time for the tongue
Unlock: Acquire the Big Drag achievement
Tongue Tied: Allows you to release survivors from your tongue (or push them away if they are close enough) and make a quick getaway
Unlock: After a survivor has been freed from the grasp of your tongue, survive until your tongue has re-charged
Misty Dilemma: The cloud that surrounds you while you are alive is much harder to spot, and you dont have insects buzzing around you
Unlock: Acquire both the Chain Smoker, and Big drag achievements
Iron Gut: +200 health, No explosion on death
Unlock: Vomit on a survivor and survive until your bile has recharged
Critical Mass: -49 health, decrease in the distance needed to fall to pop and rather than firing bile, activating primary fire causes you to explode instantly
Unlock: Explode on survivors 10 times
Stomach Upset: 35% larger Spread of Bile
Unlock: Acquire the Barf bagged achievement
Fast Digestion: -30% recharge time for bile
Weak Colon: Attacking in melee causes you to leave a fart cloud which attracts a small amount of common infected from the surrounding area to that location, even if survivors werent hit by the attack. The infected fight among themselves if there were no survivors found at that location.