History Videogame / Left4dead2

** The M79 grenade launcher, which requires much practice to use effectively – that is, kill as many infected as possible without blowing your own team up in the process. It is the only weapon that has splash damage outside of grenades which in theory makes it great against hordes; additionally, it will one-shot most special infected with a direct hit and stagger them with a near miss. It also deals extra damage against Tanks, killing them in four hits on regular difficulty. However, the slow speed and arcing trajectory of its projectiles makes it difficult to hit moving targets at long range, and the explosion radius is just small enough to make it very easy to miss. Furthermore, it is a liability in close quarters, detonating on contact with the first object or surface it hits: unless you are on elevated ground, you will likely end up hitting yourself and your teammates. It also reloads very slowly after each shot. As with all special weapons, the grenade launcher cannot be refilled at ammo piles, though its generous reserve of 31 rounds makes it rather more forgiving than the other two.

* TakeUpMySword: During The Passing, you also find an assault rifle in the hands of [[spoiler: a deceased Bill.]] You can pick it up and finish the job that they started.

** Realism mode is a setting independent of the standard difficulty settings. This mode removes all the auras allowing you to locate other survivors, items, and infected which are pummeling other survivors. Commons take less damage when shot anywhere except the head, and survivors only respawn at [[{{Checkpoint}} Safe Rooms]]. It can also be set to [[NintendoHard Expert mode,]] which gives you an [[BraggingRightsReward achievement]] if you manage to survive. One odd quirk of the mode: the magnum still instantly kills ordinary infected with body shots, which greatly increases its value; an early magnum can make a big difference in survivability.

* NintendoHard: Many Mutation gametypes.
** Last Man On Earth removes all common infected... as well as the other three survivors. The only saving grace is that you'll revive automatically after being stunned to incapacitation by a Hunter, Smoker, Jockey, and Charger. Otherwise... you have to repeat the stage until you give up or succeed.
** Hard Eight causes eight special infected to spawn at once.
** Special Delivery eliminates common infected but [[HarderThanHard ensures a full set of]] '''''[[HarderThanHard TEN]]''''' [[HarderThanHard special infected at all times.]]
** Lone Gunman surpasses Expert damage even on Easy (ANY damage at all is game over on Expert Lone Gunman), allowing only one survivor armed with only a magnum and grenades, and spawning Boomers constantly.
** [=TAAAAAAAAAAAAAAAANNNK!!!=] plays it for fun, by removing AI-controlled special infected and having players only be survivors or Tanks. This can actually make the game much easier, as survivors can [[LeeroyJenkins just run like hell through the level]] without having to worry about being stunned by a Hunter, Smoker, Jockey, or Charger. A Co-op equivalent, Tank Run, was added in the Last Stand update, which removes common infected but makes every Special Infected spawn as a Tank. And they spawn on a timer, so multiple Tanks can be active at a time if you don't kill the previous one before the next shows up.
** Obtaining the "Strength In Numbers" achievement. To earn this, you have play Team VS or Team Scavenge with a group of your friends and beat the other team who are random players that are friends with each other. The catch? There will always be one team who will all RageQuit and screw over the other team out of earning the achievement. On top of this, Team VS/Scavenge is hardly used at all since most people prefer public games where it is easier to set up and get a game going more quickly. With rage quitting and people not playing these game modes, the achievement is pretty much unobtainable without boosting.

This was followed by the ''Left 4 Dead 2'' DLC "The Passing", which [[MassiveMultiplayerCrossover brings the original survivors and the new ones together]] (well, three of them anyway) and "The Sacrifice" for both games, which lets players choose who makes [[HeroicSacrifice the ultimate sacrifice]] and was preceded by a [[http://www.l4d.com/comic/ free comic]]. The latter update also made "No Mercy" available in the sequel, complete with the original survivors as the playable characters. Cue rumors that Valve planned to make the entire first game [[EmbeddedPrecursor available for free in the sequel]] (which they did) and more cries of the first game owners being ripped off.

* AbnormalAmmo: Frag or incendiary ammo boxes, which provide one magazine of this before switching back to regular rounds.

* AnAssKickingChristmas: Several custom survival maps are set during the holiday season.
** ''[[http://steamcommunity.com/sharedfiles/filedetails/?id=121460643 Santa can I go out and kill tonight 2]]'' makes the survivors the size of toys in a massive house full of giant presents and a frozen lake with Santa trapped inside; Bots have a tendency to [[ArtificialStupidity fall off ladders to their doom far below]]. This survival map is one of the few maps of its kind to have an actual ending; while holding off the zombies, the survivors eventually find a way to rescue Santa from the frozen lake.
** ''[[https://steamcommunity.com/sharedfiles/filedetails/?id=208903847 Last Gift]]'' has the survivors fighting endless hordes of Zombies in a beautiful town festooned with decorations. In the background, a jukebox blares the Midnight Riders' ChristmasSpecial ''All I Want For Christmas (is to kick your ass)''.

* BalconyEscape: In the first chapter of Dead Center.

* BodyHorror: The Special Infected have undergone horrible and probably quite painful mutations from ''Left 4 Dead'' to ''Left 4 Dead 2''--the Smoker especially. The new Special Infected haven't had it easier, either; just look at the [[http://images4.wikia.nocookie.net/left4dead/images/7/75/Spitter2.jpg Spitter.]]

** Even if one of them ''explodes'' after their life goes from 1 to 0, it's mostly Justified with the Special Infected, who obviously are extremely aggressive and have little-to-no self-preservation instinct left. Barring a few Specials who will duck behind a wall if they're not ready to attack you yet (before attacking you later instead, of course), they are ''going'' to come after you no matter what happens to them until ''one'' of you is dead.

* DeadHandShot: The box art.

* GrenadeLauncher: The M79.
* {{Griefer}}:

* HyperAwareness: meta example. The best ''players'' exhibit this, being aware of all the directions from which infected could attack and keeping their eyes (and ears) open for incoming specials. In comparison, the AI bots (as mentioned above) are LazyBackup with a horrific case of SelectiveObliviousness.

* RespawningEnemies: All infected excluding the Witch and Tank.

* RuleOfCool: In contrast to the previous game's more grounded finales, the finales for this game can sometimes stray into the absurdely awesome.

** The "shooting the pilot" snafu in "Swamp Fever" counts as a running gag from the original game; "Crash Course" starts off with the survivors standing at the site of a helicopter crash -- the news chopper from "No Mercy" -- and the various possible dialogues make it clear that Zoey had to kill the pilot after he turned (to which Francis is very likely to snark at her over).* ScriptedEvent: Generally not used, but there are a few such as [[spoiler: the military bombing a bridge.]]

* TakeUpMySword: If a survivor dies, another can take their gun.
** Or this might well be [[ExactlyWhatItSaysOnTheTin an actual katana.]]
** During The Passing, you also find an assault rifle in the hands of [[spoiler: a deceased Bill.]] You can pick it up and finish the job that they started.

* TechnicallyLivingZombie: The infected ''might'' still even be curable, according to the military. This is most likely wishful thinking.

* UnwinnableByDesign: One of the still-listed achievements is tied into the long-gone Valve Gift Grab 2011 event.

* VideogameSetpiece: The explosions in The Parish.

[[folder:General Media Tropes]]

* TheAloner:

* BattleInTheRain: The appropriately titled "Hard Rain" campaign forces players to fight off zombies in a raging storm.
** To a lesser extent, it is also raining in the crossover campaign "The Passing".

* DVDCommentary: Like all Valve games since ''Lost Coast'', both games have a commentary mode, where you can play a campaign that contains commentary nodes which will play commentary audio from the developers. You're locked in Easy difficulty and zombies will ignore you. Naturally, you can't earn achievements this way.

** HisNameReallyIsBarkeep: Coach never actually states whether it is or isn't his job and/or name. And if Coach dies, Rochelle may jokingly ask "do you think Coach was his first or last name?"

* IncrediblyLamePun: The characters and achievements are quite fond of these.

* RisingWaterRisingTension: ''Hard Rain'' takes place during a heavy rainfall, which intensifies with every stage. Other than limiting visibility and attracting the Infected, the levels eventually get so flooded they severely hinder movement on the ground. This prompts players to instead seek higher ground and travel along walkways and ledges to keep up the pace.
* RunningGag: Ellis' stories about Keith.
** The "shooting the pilot" snafu in "Swamp Fever" counts as a running gag from the original game; "Crash Course" starts off with the survivors standing at the site of a helicopter crash -- the news chopper from "No Mercy" -- and the various possible dialogues make it clear that Zoey had to kill the pilot after he turned (to which Francis is very likely to snark at her over).

* TheSmurfettePrinciple:
** Each group of survivors only has one female. This is [[JustifiedTrope justified]] in-universe by the genetics of the Green Flu: the carrier gene is said to come from the father, and not the mother.
** Averted by Taito's arcade adaptation of this game called ''Left 4 Dead: Survivors'', where Coach and Francis are replaced by a Japanese school girl, making for two females per group.

* ToiletHumor:
** ''The Passing'' contains a large amount of graffiti [[http://images.akamai.steamusercontent.com/ugc/40862758495330345/F3DDE615D8B991DD7B6E5933748AD6EA3F34D07A/ scribbled around a toilet]], asking if zombies poop and complaining about the lack of toilet paper.

[[folder:Meta (Community/Developer/Supplemental Material) Tropes]]
* ArtEvolution: The higher polygon count and upgraded lighting effects compared to the first.
* BagOfSpilling: {{Lampshade|Hanging}}d in the beginning of Hard Rain. After being dropped off to the Burger Tank by Virgil, the survivors realize that they left their bag of guns on the boat.
--> '''Virgil''': I'll drop the anchor just off shore, waitin' for ya. Signal at me when you get the gas.\\
'''Nick''': What are we supposed to signal him with?\\
'''Ellis''': Oh, there's flares in the gun bag.\\
'''Nick''': What gun bag?\\
'''Ellis''': You didn't grab the guns?\\
'''Nick''': Me?! Who died and made me gun monitor?\\
'''Ellis''': [[DeadpanSnarker Pretty much everybody]].
* BiteTheWaxTadpole: The zombie hand on the cover is holding up 2 fingers in the same manner as someone in the U.K. would when telling you to do something unpleasant... Apart from the UK version, where the hand is photographed from the other side, making a "victory" sign.
* BloodierAndGorier: Mowing down the Infected wasn't necessarily a clean ordeal in the first game, but thanks to the updated gore system in this entry it's way messier and more detailed. High-caliber gunfire can tear chunks out of their torsos, poorly-aimed headshots [[JawBreaker rip off their jaws]], melee weapons leave deep slash marks, and the ''really'' big weapons can mutilate them beyond recognition.
* BodyHorror: The Special Infected have undergone horrible and probably quite painful mutations from ''Left 4 Dead'' to ''Left 4 Dead 2''--the Smoker especially. The new Special Infected haven't had it easier, either; just look at the [[http://images4.wikia.nocookie.net/left4dead/images/7/75/Spitter2.jpg Spitter.]]
* CharacterFilibuster: The other survivors have to tell Ellis to shut up whenever he rambles on about Keith (and Zoey in the "The Passing" DLC).
* DeliberatelyMonochrome: After being downed and revived twice, you see the entire world in black and white, complete with blurry peripheral vision and red item highlights. If you're not healed, you ''will'' die. The developers included this because playtesters were frustrated when inexperienced players were repeatedly going down and delaying the group.
* DirtyBusiness: In order to halt the spread of the infection and save what ever non-infected people they can, the military in TheBigEasy made it their policy to gun down carriers (people who don't turn but can spread TheVirus) by the hundreds, maybe thousands. Whether this makes them AntiHero or [[KnightTemplar Knights Templar]] is open to debate.
* DivergentCharacterEvolution: In terms of the male survivors' animations. Bill, Louis, and Francis all use virtually the same animations, whereas Coach, Ellis, and Nick have more distinct animations showing their personalities and how much experience with guns the three have.
* EasterEgg:
** In "The Parish", going up the stairs of the store-made-safehouse, you can find a door with an orange light outline.
** In the additional map "Suicide Blitz 2" you can find a strange white place called "[[VideoGame/{{Portal 2}} Aperture Science Urban Zombie Testing Facility]]" which is filled with companion cubes, zombies and [[TheCakeIsALie cake]].
* EdgeGravity: If your character steps off a ledge (or is ridden off by a Jockey), he or she will automatically dangle off the ledge, holding on with their hands for dear life for as long as they can until a teammate helps them. You can also grab onto a ledge if punted off by a Charger or Tank... if you're lucky.
* GoneHorriblyRight: The result of Valve trying to squash the game breakers from the first game; melee shoving abuse and corner camping. The sequel added new special infected to discourage survivor players from corner camping and added running events where the survivors have to move in order to stop the event. However, this backfired greatly since most survivor players will now rush the entire time in every map and rarely stop, making it difficult for infected players in versus mode to land an attack on them.
* {{Gorn}}: The damage modeling borders this, even more than the first game. Torso wounds gape, expose bones and can spill out the zombie's guts, heads may be only halfway destroyed, pipe bombs exploding a mob of enemies went from the first game's [[PinkMist cloud of red]] to a shower of assorted body parts and intestines, and anything that catches fire will have a charred appearance by the time it stops burning.
** In terms of SceneryGorn, this is somewhat averted. Just like the first game, the survivors are pitted wandering through mostly-intact but abandoned buildings, some of which still have power. Of course, this gets completely PlayedStraight as the army begin blowing up New Orleans as the survivors reach that city.
* ItsPopularNowItSucks: Invoked and played with by the Midnight Riders. Near their last known concert site, a bunch of well-wishers and mourners lament the loss of the Midnight Riders... until a graffiti says they were safely airlifted out. Then the graffiti turns to angry "they sold out and were never good" insults.
* LeeroyJenkins: Mostly applies to newbies who keep making common mistakes, such as running ahead of everyone (which usually gets them killed and are too far away to be saved in time), angering a Witch without having the right gun for it (only shotguns can kill her instantly with a well placed headshot), or flinging Molotovs like a hot potato and setting other players on fire from it.
** Oh, there's more. See the trope page itself for the huge list.
* LetsPlay: Both games have one on the Something Awful forums; the one for the second game can be found [[http://lparchive.org/Left-4-Dead-2/ here]].
* MythologyGag: [[VideoGame/{{Portal}} "Still Alive"]] can play on jukeboxes, albeit very rarely.
* OddNameOut: The folders for major updates to the game are "left4dead2_dlc1" (''The Passing''), "left4dead2_dlc2" (''The Sacrifice''), "left4dead2_dlc3" (''Cold Stream''), and "update" (''The Last Stand'').
* OnlySixFaces: Subverted with a better common infected random generation system. However, there are less face textures overall for ''2''[='=]s common infected than there were for ''1''[='=]s, and ''1''[='=]s face textures would include things like alternate hair colors and distinctively black or Asian facial features. This is especially true with ''The Last Stand'', which brings back skins cut from the first game's beta alongside its retail skins.
* OurZombiesAreDifferent: Of the infected, easily-enraged sort much like in ''Film/TwentyEightDaysLater'' and various types of {{Elite Zombie}}s.
* PreorderBonus: The baseball bat weapon, which spawned in the start of every single campaign and people who didn't preorder could still use the bat as long as a player on the team had preordered. When The Passing DLC was released, baseball bats now randomly spawn in the maps with other weapons instead of always being in the start.
* PoorCommunicationKills: This will literally be your game-ender online if you or the rest of your team fail to talk or at least call for help if being pinned by the infected, especially in Realism and Realism Versus modes where you can't spot each other with glows anymore. Lots of games have been lost due to people simply not speaking up.
* PreviousPlayerCharacterCameo: The main draw of ''The Passing'' is seeing the new survivors and the old ones [[spoiler:minus Bill]] in the same place interacting with one another. The old group will even cover the new ones in the finale from the bridge.
* SeriousBusiness: Handfuls of people take the game very seriously and will scream at you or call a vote to get you booted if you do anything they don't like (and not in the sense that the target of their wrath is being TooDumbToLive, either). More noticeable in VS mode where people will yell at you for not saving them from the infected quick enough and/or yell at you if you don't do enough damage to survivors or just plain outright miss your attacks. [[note]]In fact, in most Versus games, when someone becomes the Tank, all the infected players put all their hopes on the Tank player and expect him or her to to kill the Survivors in one go. What most people don't realize that the Tank alone cannot kill the Survivors unless the players are extremely stupid and the Tank needs support from the other infected. If you're the Tank and get caught on fire or die without killing at least one player, expect most people to call you a fail Tank.[[/note]]
* SlidingScaleOfContinuity: The game is pretty firmly level 3 (Subtle Continuity), with the start of the next area being a direct result of what happened at the end of the last. For example: fueling up a race car to escape from a zombie infested mall only results in them abandoning the car when they reach blocked traffic, thus having to travel through a dilapidated carnival on foot.
* SuperpowerLottery: As far as zombies go, the Tank and Witch have won this. Versus mode takes the trope literally where if a Tank spawns, a random player on the infected team will be chosen to play as the Tank.
* TakeThat: In the 2nd map of The Passing, when approaching the stairwell leading into the sewers, there's a sign that says the rest of the underground tour will be finished in the year 2010. Rochelle or Coach may quip about how the first phase is nowhere near finished and wonder how there can be a phase 2 already. This is a jab at the fan base that cried out how ''Left 4 Dead'' wasn't finished when ''Left 4 Dead 2'' was announced.
* TheVirus: If you're... unlucky enough, you turn into a constantly crying, always-guilty Witch, a head humping horny midget, an acid spitting hag, a giant armed freak, an exploding fatass, get Gene Simmon's tongue, become a flying Parkour expert, or turn into the [[ComicBook/TheIncredibleHulk Hulk]].
* WhamLine: For many an Infected team, seeing "You will become the Tank - Get ready to attack the survivors"[[note]]or "Someone is about to become the Tank" if you aren't chosen[[/note]] means that [[ThisIsGonnaSuck shit is about to get real]], as a Tank's actions (and the Survivors' response to it) can singlehandedly make or break a Versus round.
[[/folder]]

[[folder:Gameplay Tropes]]
* AIBreaker: Tanks normally attack and chase the closest survivor. If said survivor is standing next to an incapacitated survivor, the Tank will choose to beat on the downed survivor while ignoring the healthy one[[note]]due to collision checks, this also happens with human players in Versus mode, so the trick also works on inexperienced Infected players[[/note]]. Players knowing this can use the downed survivor as a decoy while the rest wail on the Tank. This isn't as effective on Expert difficulty, due to the Tank's boosted damage output.
* AntiFrustrationFeature:
** Getting hit by a flying car punched by a Tank normally incapacitates you instantly. The finale of The Parish has the bridge filled with cars and a Tank will spawn halfway through the trek. For this level only, a car punched by a Tank will only cause major damage instead of an instant knockdown.
** Incapacitated survivors no longer deal friendly fire damage, letting you blast away from the ground to cover your rescuer without fear of accidentally bringing them down as well.
** Survivor bots will never carry melee weapons. This is likely due to them treating secondary weapons as pistols (as a remnant from importing the AI from Counter-Strike: Source), thus them attempting to use a melee weapon at range is averted in practice.
** As a Survivor is standing up from being pinned by a Special Infected, the Survivor is completely immune from all forms of damage, including things like Commons attacking in a group and a Spitter pool that was shot underneath you (the Survivor ''can'' be pinned by a different Special, however). This is because the Survivor is locked in place for a few seconds, which would normally make them an easy target for cheap shots.
** The infected can never trigger car alarms, despite the undead jumping all over cars on the regular. Likewise, Tanks can't trigger car alarms – if a Tank punches an alarmed car, the alarm is permanently disabled.
** The Headshot mutation enforces a rule where [[ExactlyWhatItSaysOnTheTin common infected can only be killed with headshots]]. Riot infected are exempt from this rule since their only weak spot are their backs.
** The Last Man on Earth mutation alters the special infected behavior where, if you get pinned by a Smoker, Hunter, Jockey, or Charger, they will back off once they reduce your health to zero and the player automatically revives in black-and-white mode so that you can regain your bearings. However, this mercy is not given if you get incapacitated by any other means.
** A Spitter's spit that lands in an elevator will leave behind a much smaller pool and will fizzle out more quickly so that the survivors aren't cheap-shotted when the doors are closing in. Similarly, if a Spitter is killed inside an elevator, the pool doesn't spawn at all.
** For any fall that a player is required to take, fall damage is disabled, even if the player jumps in the air before taking the fall. This includes instances like the gully slide outside the motel in Dark Carnival, the tallest drop of the rollercoaster, and the drops into the sewers in both The Passing and The Parish.
** If a survivor is trying to help an incapacitated teammate up, the process will normally be interrupted if either survivor is hit by a Common Infected. AI survivors are not subject to this, and can get you back on your feet even with a horde wailing on them (or you).
** When playing single-player, Scavenge finales do not require you to collect all of the gas cans, to compensate for the survivor AI not being coded to do so.[[note]]This does ''not'' apply if you're in an online mode and happen to be playing alone, at which point Advanced difficulty requires every can on the map[[/note]]
** Survivor bots cannot set off alarmed cars, even if they jump on top of them. However, they fire their guns less around alarmed cars anyway, which offsets the immunity.
** The Director isn't merciless when it comes to Witch spawns and behavior;
*** Much as Survivor bots can't set off alarmed cars, they also cannot startle a Wandering Witch with gunfire (they can still startle her by running into her, but this is far less likely of an occurrence). If anything, a bot shooting a Wandering Witch is actually helpful, as they still scream for a split second and narrow down their position relative to you.
*** While this is not as strict of a rule, Witches and Tanks usually don't spawn in the same place, meaning you won't have to worry about watching your step and your fire while the strongest enemy in the game is running after you. Even if a Tank spawns in the Sugar Mill, the area he's in is usually cleared of Witches.
*** Speaking of the Sugar Mill, there are far fewer Witches in Versus Mode than there are in the regular campaign (though there will still be 3-4 as opposed to a regular level's 1-2), which makes up for the fact that the Special Infected are now controlled by players. However, to compensate, you cannot earn the Achievement "Sob Story"[[note]]Reach the Sugar Mill's safe room without killing any Witches[[/note]] in Versus.
*** Witches can spawn in regular Crescendo Event areas (and they can even spawn directly in the path required for a gauntlet), but they cannot spawn in the location of a Finale (though they can spawn at some point during the level, they can't spawn in the actual area you will be fighting the final Horde in). Even if a Witch is modded into a Finale, it will always be sitting down (even in the Parish and Dead Center, where they would otherwise be standing up).
** When a survivor dies, their main gun and all other items are dropped except for their secondary weapon (pistol/magnum or melee weapon) so that if the dead survivor is brought back to life with the defibrillator, they'll still have a weapon to defend themselves with in the event that their fellow survivors looted their corpse previously.
* ArmorIsUseless: Averted by the riot cop zombies, who can endure anything other than explosions or fire; [[AttackItsWeakpoint so long as it strikes them in the front.]] Rather hilariously played straight when you throw a molotov at them, since that's what real riot armor is built to withstand.
* ArtificialBrilliance: While the Special Infected can be quite stupid at times, it doesn't happen too often.
** Most of the times, they are quite smart and are very wary of the presence of the players. Hunters and Boomers will always try to hide around corners or behind thick shrubs so that they can ambush the players. The two may also tag team players if a player is caught by a Smoker. Smokers and Spitters will attempt to run away if their attack fails and Hunters will escape by repeatedly jumping away if they are shot at from a distance. Generally speaking, the Specials all try to get to places that the survivors can't reach easily before attacking or after being spotted.
** Tanks are now much smarter than in the original. They try to avoid fire the player makes, assuming the player sets the fire off too early. When they down someone, they will usually go chase the other survivors instead of just pounding one till they're dead and become a sitting duck. Though pounding one of the survivors to death is occasionally a smart move and somewhat terrifying, there's a reason you were never encouraged to do that in versus.
** The Common Infected themselves show signs of this - instead of running straight towards the Survivor, they tend to run around in circles, avoiding bullets while attacking the Survivors to the sides or even the back.
** A simple matter, but AI survivors will [[NeverSplitTheParty usually pair up with them if two human players split up]]. Additionally, if two human players stand back-to-back during a horde event, the other two will usually cover the two remaining sides, creating a diamond formation that covers all four directions.
** Though the Survivor AI has many infamous quirks, they handle Boomers excellently; they will rarely if ever shoot one if doing so will cover someone in bile, and they're specifically programmed to shove it back and then ''step'' further back if they're at risk of being exploded on, meaning they handle Boomers in basically the same way a player would.
* ArtificialStupidity: Although it could be a good deal worse, a bot Survivor's AI has many infamous quirks. This is a great reason to play the game with actual people. See [[https://www.youtube.com/watch?v=VqyNS7ZdY1A this YouTube video]] as a hilariously shameful example from around release.
** The AI seems to have been improved since the first game, though some of the achievements cause it trouble. Of particular note is the "Sob Story" achievement, requiring the player to complete a stage without killing a Witch. The AI is not remotely suited to sneaking missions.
** Survivor bots are absolutely ''hopeless'' with scoped rifles. They never use the scopes to begin with, and since their AI patterns are mostly inherited from Counter-Strike, they'll all too frequently switch to their secondary weapons when an enemy gets up close. Since this is a zombie game, the odds of this happening are ''extremely'' high. This more often than not results in said bot having the least amount of kills by a mile (especially if the bot is Ellis, whose preferred weapon type are scoped rifles). Too often there will be instances of a player getting caught by a Charger, and said bot resorts to dinky little pistols rather than using the scoped rifle which would kill that Charger far more quickly. Survivor bots using shotguns tend to do this in reverse, switching to pistols if they spot an enemy to fight that's far away, but that's far more beneficial as said enemies are usually not a threat at that distance and it helps the bot preserve precious shotgun ammo.
** The Chainsaw Massacre mutation amplifies the survivor bot's stupidity to new levels. They will either run ahead or lag badly behind and not do too well in saving you from special infected. This was corrected later causing the AI to rarely stray far from players, but they still have issues, the main one being the bots' ineptitude with melee weapons.
** Survivor bots can't see through scenery and have a [[TheGuardsMustBeCrazy disturbingly short attention span]]. In versus mode, the survivor bots will [[NoObjectPermanence quickly forget]] about special infected if they so much as [[FailedASpotCheck crouch behind a car]].
** When near car alarms survivor bots will very much hesitate to use their guns, even when being attacked by a single zombie. This is to mimic player patterns to avoid hitting the car alarm, but since the weapons of survivor bots are FriendlyFireproof, this is a needless redundancy. It's probably better to set it off and get them to fight back again.
** If a Jockey grabs on to you, the AI rarely, if ever, just shoots the Jockey, and when they do, they'll try to target the Jockey from close range and miss horribly instead of, y'know, shoving the Jockey off. The tendency for computer-controlled Jockeys to [[TheComputerIsACheatingBastard randomly decide they can't be killed until they've at least done some damage to a survivor]] doesn't help.
*** A similar case also happens for Smokers. In the first game, the survivor bots would usually be really quick in saving someone caught by a Smoker. In the sequel, they now will sometimes ''wait'' until you take damage before they free you. In the worst case scenario, they'll ''sit and watch'' as the Smoker chokes you to death, not even ''bothering'' to shove the tongue off. Additionally, even though every Survivor has lines referring to "shooting the tongue", they never attempt this strategy at all, so if they can't see the Smoker, you're a sitting duck until they catch up to you.
** It gets pretty close to SpitefulAI: survivor bots always place human players between themselves and their target so they can [[FriendlyFireproof shoot through the players and throw off their aim]], they [[FantasticRacism typically take forever to rescue humans from special infected but immediately drop everything if another survivor bot is in danger]], and if they manage to piss off a Witch they will once again place the player between them and said Witch, presumably in the hopes that it goes after the player instead.[[note]]The worst bit? Most of this was the result of a patch that actually ''upgraded'' the AI; previously they had been just TooDumbToLive.[[/note]]
** Whenever you encounter a Spitter, bots will make no attempt to avoid their acid until they've already stuck their feet in it.
** Even garden-variety Common Infected can give the survivor bots trouble. If they get mobbed by Commons, the AI has an alarmingly high chance to just stand there and blindly shove in all directions without even bothering to try and shoot or run, inevitably getting mauled in the process.
** If the bots get close to the safe room, they make a beeline for it and stay there regardless of the threat level in the immediate surroundings. This can lead to you getting pounded to death by a Tank and swarms of infected while the bots cower in the safe room. Doubly annoying considering that in most other situations, the bots are too dumb to keep up with you if you aren't constantly stopping and looking over your shoulder. This also means that if a Witch is either in the safe room or right by it, she ''will'' get startled, and the bot will have nowhere to run.
** And lastly, Survivor Bots are specifically programmed not to mess with throwables like bile bombs, gas canisters and molotovs. This would probably be a blessing if not for the fact that that the two "Scavenge" finales involve [[FetchQuest collecting them]]... and [[TimedMission spawn higher densities of zombies if you take too long]]. Mercifully, these finales also require less gas cans to complete in single player mode to offset the fact that you'll be doing literally all the work.
** If you play in single player mode often, {{Game Mod}}s such as [[https://steamcommunity.com/sharedfiles/filedetails/?id=2279814689 Left 4 Bots: Improved Bots]] are a good way to avoid breaking your monitor in frustration. They're still not nearly as good as good human players, though it helps that their reaction time to being pinned or snagged is shorter, they can grab and use throwables, share items, and even in custom maps they hardly get stuck because of bad path-finding. The linked mod also allows to have bots take over being the leader along with returning the leader role to player in case of getting stuck, ability to use "warp" chat command to teleport survivor bots to your location, and added feature for bots to be able to scavenge gas cans in campaign stages with scavenge objectives.
** As of the Last Stand update, Survivor bots AI are noticeably improved, like how they maintain a great deal of distance to minimize friendly fire, defeats infected, common and special alike, faster, almost never visibly teleporting (a known pathfinding issue workaround), as well as visibly improved reaction time. However, they have some quirks like prioritizing killing special infected over bashing survivors to save them (such as Smoker, if the Smoker is out of AI Survivor's line of fire, then it's a large chance that the bound survivor is left for dead). The distancing might also cause problems on several custom maps, where they won't close in on small boxed areas like escape points or elevators (due to fixes on nav files, the official campaigns has no issues), making it possible to get stuck.
* AuraVision: Used to find teammates (and bile-bombed Infected) as well as nearby items as Survivors and used by Infected to see where Survivors are going and what health level they're at. Averted in Realism mode.
* AwesomeButImpractical: The mounted machine guns available in certain areas (most notably the finales of The Sacrifice and Swamp Fever) are bar none the most powerful weapons in the game, being able to take down Tanks in a short period of time, have unlimited ammo, and never need to reload. However, they're often placed in inconvenient locations, only swivel around a 180 degree arc (meaning that your backside is completely exposed), you must stand completely still to use it (leaving you at the mercy of Spitters, Hunters, Chargers in your blind spots), shooting it for too long will cause it to overheat and render it useless for an entire minute, and Tanks will ''still'' come after you and throw rocks at you, the latter throwing you off the machine gun and making you a sitting duck. In fact, Tanks are [[ArtificialBrilliance specifically programmed to go after the Survivor on the mounted machine gun ''first'',]] though [[ArtificialStupidity this can also be exploited to draw aggro.]] As a result, it's often more convenient to get down and dirty the old fashioned way, but Louis handles it just fine in The Passing. In short, use it if you can, but do so at your own risk.
* BackStab: Shoving an idle, unaware Common from behind is a OneHitKill.
* BadBoss: The Director (if it can be considered the Infected's boss) in Versus mode hates Infected players even more than the Survivors, spraying the map with first aid kit spawns and often not bothering to send a horde after a Boomer attack.
* BattleInTheRain: The ''Hard Rain'' and ''The Passing'' campaigns both feature rain. In ''Hard Rain'' it starts off as a drizzle and evolves into a hurricane, with random bursts of extreme rainfall and gale winds that [[InterfaceScrew make it difficult to see and hear]]; the rain intensity in ''The Passing'' is randomly selected by The Director at the start.
* BlackoutBasement: The official campaigns do a good job of averting this in favor of {{Chiaroscuro}} lighting, but all bets are off with custom campaigns (one of which is titled the exact name of the trope).
* BlatantItemPlacement: Zigzagged. A lot of guns are found by dead survivors, Whitaker's gun store, security room gun lockers, or a suitcase that contains money as well as pistols, explosive items are usually found near generators, and axes, crow bars and guitars spawn where they'd be used. But on the other hand, a lot of items spawn in very ''illogical'' places. There's massive heaps of Ammo in meeting rooms, sewers or in a certain bathroom, pills can spawn in urinals, a motel is full of jars of bile and pipe bombs, the store next to Whitaker's usually has a Molotov. There are entire lockers full of Molotovs or Pipebombs in various buildings, and just past a wedding are several tents full of guns. Whispering Oaks has a bizarre number of guns for a kids theme-park, explosive ammo and incendiary ammo just spawn in the back of trucks, there's almost no reason for a really sharp katana to spawn ''anywhere'', the list just goes on.
* BoomHeadshot: Played straight, to YourHeadAsplode levels with common infected if you use a caliber bigger than pistol ammo. Headshots instantly kill Common Infected and deal greatly increased damage to Specials, and on higher difficulties and Realism most Infected take reduced damage if shot in anywhere but the head. Mercilessly averted with the Tank, which takes no extra damage from headshots.
* BottomlessMagazines:
** The players must reload, but they have endless ammunition for their sidearms and ammo piles provide infinite replenishment for non-unique primary weapons[[labelnote:*]]anything except the [=M60=] machine gun and GrenadeLauncher[[/labelnote]].
** Exaggerated in the ''Gib Fest'' Mutation gametype, which gives all four survivors [[MoreDakka an M60 machine gun]] with infinite ammo.
* BottomlessPits: The two main forms are long drops (like the balcony of the Hotel in ''Dead Center'') and deep water (namely ''Swamp Fever''). Watch for Chargers around these.
* CallingYourAttacks: Played straight by survivors throwing grenades, invoked with the special infected's vocalizations giving them away.
* CameraPerspectiveSwitch: The game is mostly played in first person view, but the camera will switch to third person view when the player is doing an action or is pinned by a special infected.
* ChallengeRun: On top of several VideoGameAchievements, there's the Mutation mode which adds different mechanics for players to tackle. Challenges include the whole team being forced to use swords only (Four Swordsmen), doing a solo run with the Magnum only (Lone Gunman), playing a VS game where all special infected are buffed up Jockeys (Riding My Survivor), and many others.
* ChandlersLaw: The Director AI pulls this quite frequently: stay in one place too long instead of advancing and you'll get a bunch of Special Infected coming at you.
** It's also more likely to send a Zombie Horde at the Survivors at any given moment the slower they're progressing through the level. This can be something of a vicious cycle when playing on Expert.
* ChekhovsGun: In the first chapter of ''The Dark Carnival'' campaign, a jar of Boomer Bile will often spawn in the same spot. Almost no other jars spawn for the rest of the entire campaign. If you keep that jar till the end of the fourth chapter, it can be used to almost completely bypass an incredibly tough gauntlet right before that chapter's safe room.
* CherryTapping: It's possible to kill even the Special Infected, except Tanks, Witches, and Chargers, just with the secondary melee attack. Just don't [[TooDumbToLive try it on the]] [[ActionBomb Boomer.]]
* {{Chiaroscuro}}: Actively exploited by the developers to guide the players, after they noticed playtesters' [[DarknessEqualsDeath tendency to move toward the brightly lit areas]].
* TheComputerIsACheatingBastard:
** Unusual, in that the Director is supposed to be continuously tweaking the challenge of the game up and down based on how well the players are doing. However, on Expert, its moments of mercy are '''''extremely''''' brief.
** This goes for the survivor bots too, as they have aimbot accuracy, and cannot directly cause friendly fire(being able to literally shoot through others) yet chide you (and add it to the friendly fire incident list in the end results) for doing it because of how often AI survivors running around especially in panic events. [[JustifiedTrope It works]], as a half-decent human player is still more efficient overall (due to other factors like bots not being able to use grenades or any particular strategy beyond shooting things), yet a team isn't completely screwed if a player leaves mid-game.
** Under certain conditions, survivor bots will grab items ''through walls''. Players can't.
** ''[=L4D2=]'' has been accused of adding a degree of FakeDifficulty by multiple special infected spawns in campaign modes, but these are glitches... The [[{{HarderThanHard}} Hard Eight]] Mutation notwithstanding.
** AI Tank rocks, affectionately called "rofl rocks" can [[https://www.youtube.com/watch?v=FkmAna8Tg5c#t=3m31s clip through some geometry]] in order to reach a player.
** Any special infected (other than Witches or Tanks) can slash you with their claws if you manage to shove them. No "attacking while staggering" animation or anything, blood literally just pulls itself out of your chest.
** In co-op and other modes where the special infected are AI-controlled, the specials can spawn inside the safe room at the end of the level, leading to [[{{GameOver}} fun times]]. In versus, where the specials are human-controlled, you cannot spawn in the ending safe room.
* CriticalExistenceFailure:
** Averted with the survivors. When seriously injured, you run slower, jump lower. After taking pain pills, or having just been revived by a teammate, your health is constantly dropping, and at 1 [=HP=] you slow to a crawl. If your health gets taken all the way out and you're not on your "last down", you drop to the ground, only able to use pistols, and slowly bleed out until you die or are revived by an ally.
** Played straight with the common infected. Play long enough and you'll see a zombie run up to you that has had [[OnlyAFleshWound both of its arms shot off]]. (What does it plan to do then, bite you?)
** Even if one of them ''explodes'' after their life goes from 1 to 0, it's mostly Justified with the Special Infected, who obviously are extremely aggressive and have little-to-no self-preservation instinct left. Barring a few Specials who will duck behind a wall if they're not ready to attack you yet (before attacking you later instead, of course), they are ''going'' to come after you no matter what happens to them until ''one'' of you is dead.
* DamageSpongeBoss: Tanks, full stop. Four Survivors starting a level have a group total of 400 HP. On Normal difficulty, the Tank has ''4,000''.
* DeathCourse: The finale to ''The Parish'' differs from [[HoldTheLine the others]] tasks the survivors with racing across a bridge to a waiting military helicopter while fighting off continuously-spawning waves of zombies.
* DeathIsASlapOnTheWrist: Dying does not mean you are forever gone from the game. You will just respawn in a closet, come back in the next map, or get revived on the spot from a defibrillator. Versus and Realism modes prevent you from coming back until the next map and dying during a finale on any mode gets you KilledOffForReal.
* DeathIsCheap: You can be [[MagicalDefibrillator revived on the spot by a defibrillator]], rescued from a closet in campaign mode, or just simply respawn in the saferoom in the next chapter.
** The ''Ironman'' Mutation gametype attempts to avert this, but only removes saferoom respawns.
* DeathOrGloryAttack: [=Cr0wning=] (headshotting) the Witch. If you succeed, you've eliminated a very dangerous enemy instantly. If your aim is just a bit off, said dangerous enemy is now standing less than a foot in front of you taking a swing.
* DifficultButAwesome:
** The grenade launcher can clear out hordes with one well placed shot, make most special infected stumble (making it great to free pinned survivors without worrying about accuracy), and a direct hit to the Witch can make her stumble and buy you time to get away or kill her quickly. The difficulty in using the weapon is you have to reload after every shot (and each reload takes about 4 seconds) and you can't get more ammo for the grenade launcher. Unless you are skilled enough, you may cause lots of friendly fire damage to yourself or the team. You will be using your pistols or melee weapons a lot to make up for the grenade launcher's weaknesses.
** It is entirely possible to counter every single Special Infected's pinning attack (Smoker's tongue, Hunter's pounce, Jockey's riding, etc) with a well placed shove, shot or slice. Even the Charger, which normally takes two melee swings to kill, can be slain mid-charge by a well-placed melee swing to the head. However, the window for you to perform these actions are measured in ''a fraction of a second'', but it feels completely awesome to do so.
** The Tonfa is the fastest melee weapon out of the entire melee weapon set. It swings very fast, but it's blunt and has a narrow swing arc, which makes it difficult to consistently hit zombies that are swarming you.
* DualBoss:
** Unlike most campaigns, the finale of ''Swamp Fever'' will spawn two Tanks at the same time near the end, which both have to be fought in an area filled with confined spaces.
** The finale of ''The Passing'' throws Tanks at the survivors in pairs to offset the increased firepower from both groups of survivors being in play.
* EliteMooks: Pretty much ''every'' common infected becomes one on Expert Realism difficulty, the "'''REAL''' zombie apocalypse" as it's advertised. To put it into perspective, on Normal difficulty one survivor can hold off and kill over a dozen commons in close quarters without much difficulty. On Expert, a single common infected can potentially down or kill multiple survivors if they're not paying attention. To make it even better, they still appear in huge numbers. Likewise on Expert Realism, commons are tough to bring down with anything other than headshots, capable of surviving multiple point-blank torso shots from assault shotguns before biting the dust.
** Also the "Uncommon" infected that appear in certain campaigns, which are generally tougher than their common counterparts.
* EnemySummoner: The [[MonsterClown zombies dressed as clowns]], in addition to the Boomers.
* EscortMission: Played with with the "Guardin' Gnome" achievement, which is earned by winning the garden gnome from the shooting gallery in ''Dark Carnival'' and carrying it through the rest of the campaign and onto the rescue chopper.
* ExplodingBarrels: Gas cans, propane tanks, oxygen tanks, boxes of fireworks, and actual barrels in ''the Sacrifice'' campaign.
* FallingIntoTheCockpit: Versus mode, infected team. While a player can run through the campaign mode to build up their survivor skills before going in, infected players have to learn it all on the fly for their randomly assigned characters.
* FakeDifficulty: The Hard Eight and Special Delivery mutations spawn Special Infected at an increased rate, which is a good challenge for players who know how to deal with each Special and move along. Unfortunately, Spitters tend to be spammed, especially in tight spots, which forces you to either run through its acid or wait it out (a terrible idea with the constant stream of powerful zombies). And if you do the latter, chances are another one will spawn ''immediately'' after it dissipates.
* FatalFireworks: The finale of ''Dark Carnival'' gives players a number of fireworks boxes that function the same as gas cans, covering the ground in a hazard zone that ignites anything that walks into it. The spark jets on the stage can also set infected on fire when activated.
* FetchQuest: The Streets chapter of ''Dead Center'' require the survivors carry a sixpack of cola, carrying the gnome to the helicopter in ''Dark Carnival'' gives players an achievement, and there have been a few Mutation gametypes requiring the gnome.
* GameMod: From adding extra custom campaigns to correcting scripts like bot behavior or gun realism, and including changing the flashlight's texture so that it becomes useful [[RuleOfFunny or funny]], these add-ons were always popular in the game. The Workshop update made them even more so due to the ease to install and manage them.
** [[https://steamcommunity.com/sharedfiles/filedetails/?id=2250557219 Left 4 Grief]] mod, made by the same maker as "Left 4 Bots: Improved bots", allow the player to turn off friendly fire completely for all supported gameplay modes (including single player) along with several minor new gameplay tweaks such as punishing "rushers" and make friendly fire bounce back damage if enabled.
* GenreSavvy: Nick asks the group, after they reach the hotel elevator in Dead Center, if anyone has been bitten. [[WrongGenreSavvy Not that he's on the right track asking this]], as they're all immune[[labelnote:+]]technically, asymptomatic carriers[[/labelnote]], the disease has airborne mutations, and quite frankly there's a pretty low chance of them ''not'' getting bitten anyway.
--> '''Nick:''' Did anyone get bit? Isn't this how this works?
* GoombaStomp: Jumping on a common or uncommon infected's head is instantly fatal. Doesn't apply to special infected. Physically being on top of a zombie counts as a stomp, thus an instant kill, which leads to a hilarious moment where you can literally walk over a zombie lying on the ground and kill it from just stepping on it.
* GravityBarrier: Keeps you away from a zombie breeding ground and to keep you moving along to your safehouse.
* {{Griefer}}: Given the nature of public gameplay sessions, you're guaranteed to come across them in public matches. The most common type of griefer are players that shoot their own teammates to death, which is ''extremely'' common on Expert difficulty games due to the sheer friendly fire damage.
** Playing as the infected is basically griefing the survivors ''[[RuleOfFun as the goal of the game.]]'' The griefers are getting their kicks from the game itself most of the time!
** The ''Room for One'' Mutation gametype defies the normal logic of the game by only allowing one survivor to escape and encouraging team killing.
* HarderThanHard: Expert mode is ExactlyWhatItSaysOnTheTin. Only experts can expect to survive.
** Realism mode is a setting independent of the standard difficulty settings. This mode removes all the auras allowing you to locate other survivors, items, and infected which are pummeling other survivors. Commons take less damage when shot anywhere except the head, and survivors only respawn at [[{{Checkpoint}} Safe Rooms]]. It can also be set to [[NintendoHard Expert mode,]] which gives you an [[BraggingRightsReward achievement]] if you manage to survive. One odd quirk of the mode: the magnum still instantly kills ordinary infected with body shots, which greatly increases its value; an early magnum can make a big difference in survivability.
** Apparently, Realism mode is nothing compared to Ultra Realism [[http://left4dead.wikia.com/wiki/Mutations#Unrevealed_Mutations Mode]]. [[InterfaceScrew It removes all of your HUDs]], making getting important information such as how much health you or a teammate has, what items your teammates has without directly observing them, and how much ammo you have to spare, all a big guessing game[[note]]Though due to a slight oversight, you can ''technically'' see [=UIs=] for the first two by looking at the scoreboard[[/note]].
* HealthDamageAsymmetry: Each of the survivors has up to 100 health. Besides [[ActionBomb The Boomer]] and [[ColdSniper The Spitter]], all special infected have at least twice as much, with the Tank starting out with at least 3,000, yet the survivors can pick off special infected with a few shots of the right gun, and special infected do damage slowly over time. Subverted on [[HarderThanHard Expert mode]], when it's just the damage that is symmetrical. They will happily kill you off if your team mates are distracted.
* HellIsThatNoise: Every single type of Infected has their own distinct sound/musical cue to warn you of their arrival, including a few who will switch from low growls to all-out screams or roars as soon as it has one of the Survivors in its line of sight. Because the Survivors can be overrun very quickly on just about any difficulty if they aren't being attentive enough, listening for them is so essential that you almost can't play it without the sound up reasonably high (which doesn't help a whole lot with the [[JumpScare Jump Scares]]).
* HesJustHiding: Literally. Whenever one of the guys die, they're found later trapped in locked closets (or respawn in the next saferoom). It was meant to reflect how survivors get rescued in zombie films. [[invoked]]
** Averted in the final chapter of each campaign after the rescue vehicle has been summoned. Being literally LeftForDead means that the play will be (non-canonically apart from Bill in The Sacrifice) in "memory" of those who are left for dead.
* HitAndRunTactics: This is usually the best way to deal with the Tank, by [[KillItWithFire setting it on fire with a molotov]] and/or pumping it full of lead while evading it. Just make sure that you're healthy enough that you can run fast, and that there's room to run.
* HitboxDissonance: Hitboxes for Hunters and Jockeys move in front of them when they pounce, which makes them extraordinarily difficult to knock out of the air with even the slightest bit of lag. Compounded further by how little time there is to stop a Jockey pounce.
** This game somehow just has inferior collision detection. It isn't common, but it certainly isn't rare to hear the impact and see blood fly from a zombie you just smacked in the face with a [[OneHitKill crowbar]] just ignore it and continue anyways...Even when playing offline where lag couldn't account for it.
* HoldTheLine: Occurs in all crescendos and finales(except a couple in the Parish) as well as survival mode.
* HyperAwareness: meta example. The best ''players'' exhibit this, being aware of all the directions from which infected could attack and keeping their eyes (and ears) open for incoming specials. In comparison, the AI bots (as mentioned above) are LazyBackup with a horrific case of SelectiveObliviousness.
* HyperactiveMetabolism: The various mushrooms found during the Rocketdude mutation mode. Since all health kits are replaced with pills, the only way to regain permanent health is finding and consuming mushrooms found throughout the map. Each color restores a different amount of health with white recovering the least and yellow/gold recovering the most. Green ones give a speed boost, dark blue ones give grenades, and black ones [[PoisonMushroom injure you]] while also making nearby gas cans and propane tanks explode.
* InexplicableTreasureChests: The lockers in ''The Passing''. There may a justification for when they're full of pain pills or even adrenaline, but why do people need that many ''pipe bombs and molotovs?'' And why are they found in offices, underground tours and ''weddings?''.
* InfiniteFlashlight: No matter what you have equipped, you'll have a light to see your way through, and it has a handy-dandy on/off key for when you want to be stealthy as well. The downside is that the beam is not that bright and it's full of artifacts, so it's not that good, only above "necessary" usefulness. Modders have made add-ons available where the light is made decent (more uniform and brighter) or [[RuleOfFunny goofier]].
* InstructiveLevelDesign: ''Dead Center'' is set up in a way to teach players, both new and veterans from the original, about the new additions to the game:
** In the first map, melee weapons are available right from the start and a Magnum is set to spawn early on, giving players access to the new secondaries immediately. Additionally, bile jars very frequently spawn in hotel rooms and can be dropped by the Hazmat Infected that often show up, and the stage being set in a burning highrise means [[NewWeaponTargetRange you can make good use of them by chucking them off the building or into a fire and watching the Infected eagerly run to their deaths]]. Adrenaline shots and a defibrillator are likewise guaranteed to spawn.
** The second area includes a gun shop that gives players a convenient way to try out any weapon in the game, including the new additions (even the ''Counter-Strike'' weapons as of ''The Last Stand'' can all be found in the closet next to the stairs), and also gives access to {{laser sight}}s. You also get to fight a crescendo event that requires you to find an item and return it to a specific location right after to test out your new gun.
** Because the campaign is set in broad daylight, all Witches will spawn in wandering mode, showing off their new daytime behavior.
** The finale is a Scavenge level, showing off the new game mode.
* InterfaceScrew:
** Your vision becomes [[DeliberatelyMonochrome monochrome]] with red halos for items if you're incapped twice without using a medkit.
** A variation also occurs with a lightning storm in Hard Rain. When the storm is passing overhead, players' microphones are automatically quieted, to the point the players will literally have to shout to be heard by their teammates. Using 3rd party chat programs gets around that limitation at the cost of ruining the immersion.
* InvisibleWall: Only the Infected in Versus mode will run into them, and if you get close enough they stop being invisible... instead they become labeled "wrong way!"
* ItCanThink: The Director is actually a rather well working AI system. Depending on the difficulty, it will decide when to place more zombies to hinder your efforts. On Expert difficulty, it just wants you dead and doesn't pull any punches.
* ItsQuietTooQuiet: In Last Man On Earth, not only does your survivor continually [[GoMadFromTheIsolation talk as if the other survivors are still there,]] they occasionally shout out something along the lines of "Hello?" or "Is anyone out there?".
** There is also a lack of Common Infected, which makes the gameplay overall much quieter, but also gives the eerie feeling that something else is going on...
* JustForPun: Every achievement.
* KillerGameMaster: The AI director. Particularly on Expert mode, when he stops even ''pretending'' he doesn't hate your guts.
** In ''Left 4 Dead 2'', there are some maps where the infected charge out of the safe room, or very close to it. However, the director will stop the attacks when all four players are in the room but with the door still open (but existing infected will still charge).
* LevelInReverse: The campaign Hard Rain has the second half be the levels of the first, played backwards and with a monsoon in full effect, obscuring vision and dialogue.
* LimitedLoadout: You can carry one of each item that occupies a slot, such as the following:
** Primaries: Shotguns, automatics, sniper rifles, the light machine gun, or the grenade launcher.
** Secondaries: A pistol which can be dual-wielded with another, a larger Magnum pistol, or a melee weapon.
** Kits: the token medkit, a defibrillator unit, or kits to give everyone a single magazine of explosive or incendiary ammo.
** Grenades: a Molotov cocktail, a pipebomb, or a bile bomb.
** Temporary health: a bottle of painkillers or an adrenaline shot.
* TheLoad: Completely aside from the issue of bad players, any time you engage in an EscortMission, the party is effectively reduced to three members, as the person carrying the required item cannot use their weapons without dropping the item in question or simply shoving zombies, which does very little damage.
* LoopholeAbuse: Many achievements require specific stipulations in order to be unlocked, such as beating every campaign on Expert. The same achievements are still credited if you do them in any Mutation mode, even if said mutation makes it easier to achieve (such as Gib Fest, where all Survivors have the strongest gun in the game with unlimited ammunition, or Room For One, where the players start the campaign at the Finale).
* LuckBasedMission: Depending on where enemies spawn and what types they are, along with what items you find, you can either have a smooth sailing game or a nightmare of just trying to survive.
* LudicrousGibs: The first game went more for PinkMist with Common Infected, but a better game engine allows this one to really show messy dismemberment of zombies. It also has a lot more options for scattering zombie bits across the floor, between various melee weapons, explosive ammo, and the grenade launcher.
* MadeOfPlasticine: Because of how melee weapons work, it's entirely possible, and really easy, to carve through a ZergRush with, let's say, a [[http://en.wikipedia.org/wiki/Baton_(law_enforcement) baton]]. Also, hitting a special infected with a [[FryingPanOfDoom frying pan]] will kill them in one hit, except for the Charger, who takes two hits anywhere except the head, and the Witch/Tank, who are MadeOfIron.
* MagicalDefibrillator: Capable of bringing players back from the dead.
* MajorInjuryUnderreaction: A survivor's typical response to friendly fire? Some variant on "Stop shooting me!"
* MercyInvincibility: Getting hit by a Common Infected gives you a split second of immunity to attacks from other Common Infected, so that players have a fighting chance against hordes.
* MiniGame: "Dark Carnival" has 3 games for you to play, which are the Shooting Gallery, Test Your Strength, and Whack-A-Mole with the park's mascot! They each are tied to an achievement as well. [[spoiler: They also alert a horde of zombies if you successfully complete any one of them.]]
* MoodWhiplash: Happens quite often, thanks to the automatic in-game dialogue.
--> '''Ellis:''' ...Y'all... Y'all, I'm hurt.... Look, guys, ''KIDDIELAND!''
* MookChivalry: The "Last Man on Earth" mutation makes it so that Special Infected (whose clutches you would normally need a teammate to escape) back off once they've taken off your first health bar. They're not as kind the second time around, however.
** Jockeys and Hunters may sometimes decide to stay where they are and slash you the second you get up, which may cause death due to your health being so low after getting self revived. [[OneHitKill It will often end with your death if a Hunter stays around on Expert]], as it will claw you the instant your MercyInvincibility expires.
** Occasionally, after reviving from a pinning attack (e.g. getting pounced by a Hunter), the Jockey will just flat out ignore the rule, approach you while you are getting up and ride you. Rarely the Smoker also just snares you with his tongue, though it's not as common as the Jockey situation. Chargers can also do this, though they usually turn a corner before returning to try to finish you off with a charge.
** Regardless of the above mentioned rule, if you get hit with a claw attack instead of a pouncing attack, you will go down and be forced to restart the chapter. This comes up most with Tanks, Witches, and Spitters, though the other Specials (most often Chargers due to their charging attack having a longer cool down timer) can also kill you in this way if they miss their primary attack.
* MusclesAreMeaningless: The Witch is a small girl with relatively thin limbs (apart from the vicious claws)... limbs with which she can knock you down/kill you outright faster than any other Infected. Including the muscle-mountain Tank.
* MyRulesAreNotYourRules: AI-controlled infected can spawn anywhere (even ''in direct view of a player'', which they aren't supposed to do, depending on the circumstances), melee while stumbling, climb things player-controlled infected cannot, and AI-controlled Hunters even have a lunge move players cannot perform.
* NeverSplitTheParty: The game is '''built''' on this trope. Get separated or lose track of your teammates and YouAreAlreadyDead, because four different Special Infected are capable of single-handedly immobilizing and killing you if no one's around to help.
** Occasionally averted in Expert and Versus matches when one survivor staying in the saferoom with the door closed can be the difference between success or failure.
** There are also a few jarring situations in which you have passed a PointOfNoReturn and ''cannot'' go back and help your teammates. This just reinforces the original lesson, since you are forced to soldier on short-handed.
** This spawned the meme of Karma Charger, where a random Charger would come and pounce on you if you ever leave the main group. Fittingly, the AI director prioritizes lone wolves who ditch their friends, and would actually spawn a Hunter to deal with them. Of course, this lead to players finding ways to singlehandedly counter said "karma".
* {{Nerf}}:
** In the original, players could "shiva stack" (wait in a corner or secluded room, all bunched up, and repeatedly melee). This made it nigh-on impossible to extricate them with anything other than a Tank. ''Left 4 Dead 2'' stopped stacking with the introduction of the Charger and the Spitter.
** Melee weapon damage to Tanks has been nerfed since the game's release. Damage is now 5% per hit instead of 10%, which means now that survivors will most likely have to resort to kiting now instead of everyone running up to a Tank and smashing him with four Frying Pans Of Doom.
** And the shove motion ''itself'' has been nerfed by making the fatigue mechanic (shove too many times without giving yourself time to rest and the game starts applying an increasingly longer delay before you can shove again) apply to all modes rather than just Versus. This punishes the fact that you can get completely surrounded and need to shove your way out.
** Also, auto-spawning in Versus finales being removed made it more enjoyable for the infected team and more difficult for the survivor team.
* NietzscheWannabe: A lot of the graffiti is this. It gets [[DeadpanSnarker shot down]] by both the cast and other graffiti.
* NintendoHard: Many Mutation gametypes.
** Last Man On Earth removes all common infected... as well as the other three survivors. The only saving grace is that you'll revive automatically after being stunned to incapacitation by a Hunter, Smoker, Jockey, and Charger. Otherwise... you have to repeat the stage until you give up or succeed.
** Hard Eight causes eight special infected to spawn at once.
** Special Delivery eliminates common infected but [[HarderThanHard ensures a full set of]] '''''[[HarderThanHard TEN]]''''' [[HarderThanHard special infected at all times.]]
** Lone Gunman surpasses Expert damage even on Easy (ANY damage at all is game over on Expert Lone Gunman), allowing only one survivor armed with only a magnum and grenades, and spawning Boomers constantly.
** [=TAAAAAAAAAAAAAAAANNNK!!!=] plays it for fun, by removing AI-controlled special infected and having players only be survivors or Tanks. This can actually make the game much easier, as survivors can [[LeeroyJenkins just run like hell through the level]] without having to worry about being stunned by a Hunter, Smoker, Jockey, or Charger. A Co-op equivalent, Tank Run, was added in the Last Stand update, which removes common infected but makes every Special Infected spawn as a Tank. And they spawn on a timer, so multiple Tanks can be active at a time if you don't kill the previous one before the next shows up.
** Obtaining the "Strength In Numbers" achievement. To earn this, you have play Team VS or Team Scavenge with a group of your friends and beat the other team who are random players that are friends with each other. The catch? There will always be one team who will all RageQuit and screw over the other team out of earning the achievement. On top of this, Team VS/Scavenge is hardly used at all since most people prefer public games where it is easier to set up and get a game going more quickly. With rage quitting and people not playing these game modes, the achievement is pretty much unobtainable without boosting.
* NoFEMAResponse: [[NoCelebritiesWereHarmed CEDA]] tries to respond to the "Green Flu", but gets overwhelmed. Inevitably, every time the Survivors try to get to a CEDA evacuation point, it'll be destroyed with nothing but corpses to show for it, and they'll end up having to escape another way.
* NonStandardGameOver: During The Sacrifice's finale, if three of the survivors are killed, the level ends in a failure and you have to restart since you need at least two people alive for the final part since one person has to sacrifice themselves to restart the bridge and the other person has to be alive so they can escape.
* NothingIsScarier:
** Hearing a sobbing Witch and knowing she's close and you have to be careful or you'll startle her and she'll screech and try to rip you apart - and sometimes you just don't find her...
*** This is even more scary in the infamous "Hard Rain" campaign. It isn't bad enough to have 20 Witches, it isn't bad enough to have them walk around, it isn't bad enough that all but three of the Special Infected can push you into one (and will appear absolutely out of nowhere), and it also isn't bad enough to have to fight Tanks during this, but they also had to throw in the sugar cane fields (where your vision is reduced to about 2 feet in front of you).
*** And then it gets even worse on the way back through! Whenever the storming starts up, all the witches in the area will HOWL IN RAGE yet the odds of you actually running into one are pretty low. This continues right up until the finale, and you can never tell if that howl is on the other end of the level or just around that corner...
*** It doesn't help that the sounds made by the storm can resemble startled Witches.
** Sometimes you hear a special infected or its musical cue long before you see it or you know it's around the corner but don't want to be the guinea pig. The worse still, is when the Tank music starts playing but takes its time finding you so players are left frantically trying to spot it whilst trying to stick together or rethink their plans.
** The worst scares you can get is in the mutation "The Last Man On Earth", where it's single-player with no bots, and no common infected. It can get very eerie walking through the level alone while hearing the growls of special infected sneaking up on you, and since you're alone they are far deadlier.
*** What's even worse than that is the fact that the single character's vocal script is unchanged, meaning that they talk to thin air - even taking to specific survivors ''who aren't there anymore''.
* ObviousRulePatch: VS mode's scoring was altered to be more close and fair between teams. Left 4 Dead had scoring be sorely based on who made it to the safe room plus a multiplier and if a team got killed beforehand, their score would be a lot lower. Left 4 Dead 2 has the score be purely on distance traveled so that you still had a chance of catching up if you didn't make it to the safe room.
** Explosive ammo was removed from VS mode after some time due how easily survivors could stop attacks from the infected players with it. Defibrillators were also given a 25 point penalty for its use in VS mode so survivors are punished for having a teammate brought back to life in a way.
* ParachuteInATree: Corpses of paratroopers hanging from trees are frequently found. Upgraded weapons can be found on their bodies.
* PermanentlyMissableContent: One achievement, Beat the Rush, requires you to earn a medal in a Survival round using only melee weapons. In order to count for the achievement, the medal has to be one you didn't already have; if you got all medals in all Survival maps before getting the achievement, it becomes unobtainable.
* PoisonMushroom: The Rocketdude mutation has black mushrooms, which will inflict heavy damage on you with an explosion and cause your ears to ring, effectively making you deaf for a few seconds. Unlike other mushrooms that have their glowing outlines become visible as soon as you're in range, black mushrooms won't have their distinctive red glow appear until you're right next to them. Black mushrooms are usually placed inside doorways or other areas that you go through as the main route, forcing you to either find another way around them or risk jumping over without touching them. The finale to Dead Center has a nasty spot for a black mushroom; if a pair of gas cans spawn on the third floor near the elevator, there'll be some black mushrooms right in front of the gas cans. Touch them and the explosion will ignite the cans.
* PrettyLittleHeadshots: Headshots on Witches remain effective but lack the gruesome aftermath and OneHitKill. Unless you cr0wn one with a shotgun.
** Headshots with Tier One weapons leave the head intact. Except for the shotguns, obviously.
* RandomlyDrops: Hazmat uncommons (Dead Center and the Sacrifice) with bile jars, riot cop uncommons (the Parish) with nightsticks, and fallen survivors (the Passing) with random items. The Last Stand update also gave infected policemen, originally just a random Common Infected skin in the ''Left 4 Dead 1'' campaigns, a chance to drop nightsticks.
** During the holiday season, gift boxes were randomly dropped by special infected in VS mode, linked to an achievement and a Steam sale raffle.
* RegeneratingHealth: Inverted trope. Pills, adrenaline and getting picked up from incapacitation add a temporary buffer of XX health to your HP (differs from action to action), which disappears as time goes on.
** Played straight with the Healing Gnome mutation. All health related items are removed from the maps and the only way to heal is to hold a special gnome that regenerates health as long as you hold it. Of course, this also reduces the amount of firepower the team has.
* ReimaginingTheArtifact: Among ''Left 4 Dead 1'' 's infected models were reflective vest-wearing airport workers, something ''Left 4 Dead 2'' players are supposed to associate with the uncommon worker infected, but they were no different from any other common. With the ''Last Stand'' update giving most uncommon infected ''Left 4 Dead 1''-style models for use in its campaigns, and how they might've been working near loud airplane engines loading baggage into planes, these airport workers can now occasionally spawn with a helmet and earmuffs, repurposing them into being one of the ''[=L4D1=]'' equivalents of ''Hard Rain'' 's workers.
* RespawningEnemies: All infected excluding the Witch and Tank.
* RocketJump: The Rocketdude mutation mode is all about this. You're given a grenade launcher with infinite ammo and you can propel yourself high and far by shooting at your feet. To compensate for the flying around and self inflicted friendly fire, fall damage is disabled and friendly fire damage is set to the minimum. The mode also makes physics on objects like dumpsters and cars go flying when hit with the grenade launcher. You're also encouraged to use rocket jumps to reach healing mushrooms that cannot be reached by normal means.
* ScriptedEvent: Generally not used, but there are a few such as [[spoiler: the military bombing a bridge.]]
* SoundCodedForYourConvenience: Major gameplay-changing events (horde attacks and Tanks or Witches being startled) change the music. Special infected spawning are accompanied by their unique theme (except in Versus) and their vocalizations give them away; especially for players using surround sound.
* StandardFPSGuns: [[BottomlessMagazines Pistols, magnums (albeit played much differently than normal)]], shotguns, assault rifles, mounted machine guns, sniper rifles, grenades, and melee weapons.
* SuperDrowningSkills: Any map that has a river in it. Unlike the first game where being underwater too long would drain your health eventually, being submerged will instantly kill you.
** The only exception is when the water is knee-height, and getting incapacitated puts you below the surface. After a moment, however, you start taking a reasonably large amount of extra damage (aside from the automatic bleed-out damage) until you either begin to get picked up, or you die.
*** Also applies when crouched underneath the water in the finale area of Death Toll (originally from the first game).
** The water in ''Left 4 Dead 2'' is so fetid that it will kill an infected that's ''in ghost mode.'' Causing their corpse to pop out of thin air, natch!
* SuperMode: While not as flashy as most examples, survivors gain a minor one when taking adrenaline. In addition to giving a small amount of temporary health, it also temporarily: removes melee fatigue and lets you shove as much as you want, lets you perform actions like healing and reviving teammates faster, gives you a speed boost, and lets you ignore effects that hinder your movement speed like knee-deep water, Common Infected attacks, and low health.
* TakeUpMySword: If a survivor dies, another can take their gun.
** Or this might well be [[ExactlyWhatItSaysOnTheTin an actual katana.]]
** During The Passing, you also find an assault rifle in the hands of [[spoiler: a deceased Bill.]] You can pick it up and finish the job that they started.
* TakingYouWithMe: At certain points, a well-aimed Charger can grab a survivor and bring them both careening to instant death. A particularly hilarious situation can happen should you bait a Charger into trying this, only to step out of the way and watch as they run straight over the edge to their death far below.
* TestYourStrengthGame: There's one in the Dark Carnival campaign. You have to use adrenaline in order to beat it, which earns an achievement.
* TheLastManHeardAKnock: Although you're the only Survivor in Last Man On Earth, there are still rescue vehicle pilots and the gun store owner.
* ThingsThatGoBumpInTheNight: The Special Infected warning sounds. Especially so in Last Man On Earth.
* TotalPartyKill:
** "Hey guys! [[{{Leeroy Jenkins}} Check out my grenade launcher!]]" (Not actually that much of a problem on Normal or Easy, but God help you on anything higher.)
** A few specials can cause this singlehandedly: Tanks (especially when narrow spaces and cars get involved), Chargers ([[DisneyVillainDeath be careful around high ledges]]), and (if your team is [[TooDumbToLive spectacularly incompetent]]) Hunters.
** Averted with the Witch, who is programmed specifically to only be aggressive towards one Survivor. Not that things don't go OffTheRails anyway.
* TutorialFailure: For VS mode, the game does a poor job in explaining how to use the special infected to the fullest. During gameplay, you're only told of the basic controls and the actual tips aren't shown until the round is over. The game also encourages Tank players to rush in and attack the survivors (likely due to the mechanic where Tank players will lose their turn as the Tank if their aggression meter empties out), but this is a horrible strategy since a half competent survivor group can simply focus fire on the Tank to kill it quickly or set it on fire to put it on a death sentence.
* UnintentionallyUnwinnable:
** There's a bug in the collision detection of the rescue boat that ends ''Swamp Fever'' and ''Hard Rain''; depending on where your character is standing, this can result in them drowning as it sails out from under them. It is both [[HopeSpot depressing]] and [[YouHaveGotToBeKiddingMe hilarious]] to die in this way.
** In the [[CollectionSidequest scavenge finale]] of The Passing, the AI Director ''can'' spawn boredom hordes and specials if you take too long before talking to the first game's Survivors. If you do, activating the elevator will make the AI Director think you have lowered the bridge, and he will begin throwing the infinite Tanks and hordes at you... Even though you ''haven't'' lowered the bridge or even collected ''one'' gas can. And the best part? This doesn't reset if (when) you game-over. The only way to correct is to quit the campaign and start from the beginning.
* UniqueEnemy: Each campaign in [=L4D2=] has an "Uncommon Infected" unique to it, though the Last Stand update has made most of them spawn on more maps:
** ''Dead Center'' has infected CEDA workers, whose Hazmat suits render them impervious to flames. There is also a zombified Jimmy Gibbs, Jr., who is also immune to flame, can obscure vision with motor oil, and won't be sidetracked by pipe bombs or Boomer bile.
** ''The Passing'' has the Fallen Survivor, an infected man in militia gear who [[MetalSlime will run when attacked, has high health, is impervious to flames, and drops valuable items on death]]. There is also a Witch in a bridal dress.
** ''Dark Carnival'' has infected clowns, whose squeaky shoes attract more zombies.
** ''Swamp Fever'' has "Mud Men", who can move more quickly than other zombies, are harder to hit due to their hunched posture, and can obscure your vision with mud.
** ''Hard Rain'' has infected sugar mill workers, whose ear protection gear prevent them from being lured by pipe bombs, and whose hard hats make them more resilient to melee weapons.
** ''The Parish'' has infected riot cops, whose body armor makes them invincible to melee attacks and gunshots from the front.
* UnusableEnemyEquipment: {{Lampshaded}} by Coach when he sees the Riot gear-wearing Zombies.
-->'''Coach''': "That zombie's got armor.." [{{beat}}] "'''I''' want armor!!"
** Inverted in that some uncommon do carry usable equipment, but (being zombies) never actually use it.
* UselessItem: The oxygen tank is an explosive item that goes off a few seconds after it is shot. The infected generally won't wait for the tank to explode, making it nearly worthless to use effectively. The Last Stand update gave the oxygen tank a secondary effect where the hissing it creates after being shot will attract nearby common infected towards it like a pipe bomb, including the uncommon Worker Infected which normally [[KungFuProofMook ignore pipe bombs]], making the item more viable to use.
* UnwinnableByDesign: One of the still-listed achievements is tied into the long-gone Valve Gift Grab 2011 event.
* VideoGameCrueltyPotential: There is just something so fun about jumping on top of a lone survivor as a Hunter, laughing in delight as you tear them apart, knowing they're completely and utterly helpless.
** The VS mode is based around being as cruel as possible, as it actively encourages you to take notes during your own Survivor playthrough and consider when is the worst possible time for your particular special infected to appear, and to use it when it's your turn to be the zombies.
* VideogameSetpiece: The explosions in The Parish.
* ViolationOfCommonSense:
** Downing a whole pack of pain pills at once would be fatal in real life, but somehow is a good idea if you're low on health.
** In the zombie apocalypse, '''TRUE''' survivors don't even need to remove the cap to swallow a whole bottle of pills!
** If you get mobbed by common infected, setting yourself on fire with molotovs or blowing yourself up with a grenade launcher will usually clear your space a LOT faster than to keep shoving them away or trying to hack at them all with melee weapons. You'll suffer self inflicted friendly fire damage, but that will be small compared to trying to clear out zombies invading your space without the said methods.
** There are some cases where team killing is actually justified. If someone is about to die and there's nothing to heal with, players will usually kill the wounded survivor and then let them respawn in a closet or revive them with a defibrillator: both methods bring the Survivor back with 50 points of health. If no one speaks of this and do the deed, they could be mistaken for a {{Griefer}}. If the opportunity to fall to one's incapacitation provides itself, it's probably better to do it this way as this saves ammo.
** Melee weapons always do [[PercentDamageAttack 5% of a Tank's maximum health per hit]] (meaning 20 melee hits will kill them). This doesn't amount to much on lower difficulties, but it's certainly a lot of HP on higher ones, where the Tank's HP is doubled from Normal to Advanced & Expert. Obviously, trying to get close to a Tank when it can instantly incapacitate you [[TooDumbToLive is usually a bad idea]], but being able to deal about 1,000 damage in 2 seconds without using ammo is something worth noting.
** Riot cop zombies are ImmuneToBullets - even large sniper rifles and heavy machine guns - but go down instantly to improvised fire bombs; real riot armor is usually built with the opposite priorities.
** Due to ArtificialStupidity rendering bots unwilling to shoot when near car alarms, it may be simpler to set off the car alarm anyway to wake them up, even if it means fighting more zombies. The impound lot in the middle of The Parish takes this up to eleven.
* WeCannotGoOnWithoutYou: If there are any bots on the team in any non-Versus mode, you'll have to start the level all over again if all the human players are dead, regardless of if there is a bot player alive. It becomes mind-boggling when playing against a team of bot Survivors in versus mode and they are capable of moving through the level on their own without the guidance of a human player. Fortunately, there are {{Game Mod}}s that fix this, although sometimes [[ArtificialStupidity the only difference it makes is that you have to wait longer before restarting the level]].
* WhatTheHellPlayer: Shoot one of your fellow survivors, and they'll call you out for it with scripted responses.
** Or trigger a few car alarms in the impound lot in ''the Parish'':
-->'''Coach''': ''WILL YOU STOP SHOOTING THE GODDAMN CARS!?''
** As of the 2020 community update, they'll ''really'' call you out if you outright kill a fellow survivor:
-->'''Bill''': ''He was on our side!''
-->'''Zoey''': ''You REALLY have to be more careful!''
-->'''Louis''': ''What the hell, man?!''
-->'''Francis''': ''That was not cool!''
-->'''Nick''': ''WHAT?! This is hard enough without you helping the freaks!''
-->'''Ellis''': ''You're a sick man.''
-->'''Coach''': ''Keep goin' at em like that and you gonna be the last man on earth!''
-->'''Rochelle''': ''What is going on inside that head of yours?!''

* YouHaveOutlivedYourUsefulness: Special Infected which are stuck or otherwise unable to catch up to the Survivors will occasionally be killed off by the Director, with the death noise often being faintly audible to human players.
** Infected players can manually trigger this when they are at a certain distance behind the survivors, allowing them to skip the respawn time that would happen if they jumped off a cliff instead, and most notably allows them to keep using the same Infected instead of being assigned a new one at random.
* YourHeadAsplode: Shots to the head of regular zombies with primary weapons leave only their neck and a PinkMist.
* YouALLLookFamiliar: The basic infected actually have [[OnlySixFaces a small number of basic models]] but are made to look different with various filters, like clothing and blood spatter. The Unique infected all look exactly the same since they wear uniforms and some of the Bosses have two models in the second game (the Boomer has a female version, the Witch gets a one off version wearing a wedding dress in The Passing), but only one in the first.
* ZergRush: The AI director will send these at you at random, when a Boomer vomits on you, in pre-programmed Crescendo Events where you're forced to make a ton of noise to continue moving, or if you accidentally set off a car alarm, [[WebAnimation/ZeroPunctuation or whenever he's bored, which is]] ''[[WebAnimation/ZeroPunctuation all the time]]''. The normal infected also like to rush pipe bombs because of the smoke detector alarms rigged to them, and Boomer bile (both regular and purified) for obvious reasons. It is also possible to use a bile jar on a Tank, and there is an achievement for it.
[[/folder]]

[[folder:Weapons Tropes]]
* AbilityDepletionPenalty:
** If the .50 BMG machine gun {{overheat|ing}}s completely, it becomes inoperable for a long cooldown period.
** The autoshotgun can be reloaded one shell at a time, but completely emptying the magazine means you have to "prime" the weapon again after reloading.
* AbnormalAmmo: Frag or incendiary ammo boxes, which provide one magazine of this before switching back to regular rounds.
* AKA47: As with the first game, most guns are given generic descriptors, though a few guns, both old and new, are now referred to by their real names. Also, according to the sign in Whittaker's gun shop, the Magnum pistol in the game is a "Desert Cobra" rather than a Desert Eagle.
* AmmoUsingMeleeWeapon: The Chainsaw is the most damaging weapon in the game, able to tear through anything in the game in seconds if you're brave enough to walk up to it and hold down the trigger. But it still runs on gas, and when it runs out, it's useless. Unfortunately, there's no replenishing it, even with the containers of gasoline you'll occasional find lying around the map.
* AwesomeButImpractical:
** The minigun and mounted M2 machine gun, which can shred oncoming hordes and Tanks, are never positioned so they can effectively cover more than two of the generally five or so directions that zombies can come from in official maps. They'll also overheat after about fifteen seconds of continuous firing, rendering them unusable for an entire minute. Additionally, the M2 is rare in comparison to the previous game's minigun, only showing up in two finales out of six, and in one of those finales it spawns at a point where you're making a mad dash for the rescue vehicle already. And a Tank spawns ''behind'' it.
** The M79 grenade launcher, which requires much practice to use effectively – that is, kill as many infected as possible without blowing your own team up in the process. It is the only weapon that has splash damage outside of grenades which in theory makes it great against hordes; additionally, it will one-shot most special infected with a direct hit and stagger them with a near miss. It also deals extra damage against Tanks, killing them in four hits on regular difficulty. However, the slow speed and arcing trajectory of its projectiles makes it difficult to hit moving targets at long range, and the explosion radius is just small enough to make it very easy to miss. Furthermore, it is a liability in close quarters, detonating on contact with the first object or surface it hits: unless you are on elevated ground, you will likely end up hitting yourself and your teammates. It also reloads very slowly after each shot. As with all special weapons, the grenade launcher cannot be refilled at ammo piles, though its generous reserve of 31 rounds makes it rather more forgiving than the other two.
** The M60 machine gun fires bullets that shred infected, much like the mounted guns: its shots will gib common infected in one shot and pass through multiple bodies. Its high damage per shot, fairly rapid fire, and ammo capacity of 150 rounds will allow a player to fairly easily mow down an entire horde or tackle a Tank on their own. Its main drawback is that you cannot refill its ammo at all (not even with special ammo pickups) and you only get one full box. And once you run out, you automatically discard it, leaving you with only your secondary weapon unless a new primary happens to be on hand. It also has the same accuracy as the AK-47 (that is, [[PowerfulButInaccurate pretty bad unless you're crouching or standing still]]), making it easy to carelessly waste bullets. In official campaigns, it only spawn randomly in The Passing (the update that introduces the weapon), Cold Stream, and a guaranteed one in The Last Stand.
** The Chainsaw is the melee counterpart to the M60 machine gun; it has limited "ammo" and cannot be refilled and is discarded after it is emptied. It mows through infected like there's no tomorrow, including Witches, which it can kill without alerting. However it also takes time to rev up if you switch to it, and attracts all nearby infected to you due to the noise. Highly unadvisable to carry this weapon AND one of the above, since if you run out of ammo for both before a resupply point, all you have left is the starter pistol.
* BatterUp: Among the melee weapons, there are baseball bats and cricket bats. Sometimes a survivor will say this when they grab one.
* {{BFG}}: The M60 machine gun. Most survivors will even call it out as a "big-ass gun" or something similar. With decent fire rate and extremely high damage, the M60 can easily chew up hordes, but has a limited supply of 150 ammo that can't be restocked.
* BottomlessMagazines: For gameplay reasons, sidearms have infinite ammunition. They don't do as much damage as primary weapons and they share a slot with melee weapons, which don't have any limit either [[ChainsawGood with one exception]]. Also, they're the only weapons you can use while incapacitated and if you're holding any melee weapons, you'll temporarily get one basic pistol until you're back up again.
** Two mutations also employ this: "Chainsaw Massacre" gives the survivors infinite-fuel chainsaws, and "Gib Fest" gives them infinite-ammo M60s.
** It is possible for Gib Fest games to glitch and spawn any weapon normally. Extremely rarely, it is possible to find a Grenade Launcher. Because of the one-shot nature of the thing in normal gameplay, anyone who finds one in Gib Fest will quickly notice it ''has no firing cooldown'' [[note]]The weapon's long reload was meant to be its cooldown, meaning once Gib Fest removed its reload requirement your rate of fire is only limited by how fast the script replaces your ammo[[/note]]. Much hilarity ensues.
* ChainsawGood: The chainsaw has peerless damage dealing abilities, but has a fairly long starting time, only 60 seconds of "fuel", provides 50% damage resistance to common infected, and is replaced with a single pistol when it runs out of fuel or the user is incapped. The ''Chainsaw Massacre'' mutation is all about chainsaws: the only weapons that spawn are four chainsaws in the saferooms. They happen to have [[RuleOfFun unlimited fuel]].
* CrowbarCombatant: Taken straight from ''VideoGame/HalfLife'' with the bright red color scheme, it's about as common as the axe. One of the slower weapons in the game, but has the unique quirk of being able to literally rip a zombie's face off, if you like that sort of thing.
* DeusAxMachina: Fire axes are understandably a fairly common melee weapon, given that you're trudging through the remnants of civilization. They have a fairly slow swing rate, but the widest range in the game, making them excellent for chopping down hordes. They can even randomly be found frequently in ''Swamp Fever'' where you're mostly trudging through swamps, though the places you find them suggest they may be used as a stand-in for woodcutting axes.
* FryingPanOfDoom: One of the weapons with the slowest swing rate, although each swing is decently fast and it makes a satisfying "SPANG" on contact with a zombie skull.
* GardeningVarietyWeapon: The pitchfork, one of the new weapons added in the Last Stand DLC.
* GatlingGood: You get the odd mounted minigun here and there. It's set up so that the gunner will have to be covered by the other Survivors, though. It's also not actually ''that'' good, as while it shreds Infected like no other, it overheats after about ten to fifteen seconds of continuous fire, and takes nearly a full minute to cool back down to usable levels.
* GolfClubbing: Added with ''The Passing''. And it has the same attributes as the {{Katana|sAreJustBetter}} to boot, and just like in ''VideoGame/TeamFortress2'', it can decapitate if you aim high (you even get an achievement for beheading enough zombies with one). Unfortunately, for official campaigns, it was only found in that campaign until the Last Stand update.
* GrenadeLauncher: The M79.
* GunsAkimbo: All characters can find and dual wield a second 9mm pistol for doubled fire rate and extra ammunition in the magazines. Interestingly, unlike in the first game, where all pistols on the ground were the same model as what you started with, here the characters mix-and-match their beginning pistol (a customized P226) with an entirely different model (a lengthened Glock 26), although this does cause some issues where both guns can transform into one another, such as turning another player's dropped P226 into a Glock because you already have one, or dropping a melee weapon for a Glock found on a table and somehow getting a P226 from it.
* HandCannon: The Magnum is a powerful enough sidearm to practically be a primary weapon, killing all common infected in one hit and most special infected in two or three - even in Realism mode, where even the common infected are tough enough to tank two or three shots from the otherwise-similarly-powerful scoped rifles. Its only real downsides are very poor accuracy when moving, high recoil, and a small magazine, making it rather ineffective against infected with large amounts of health, like Tanks and Chargers, or against large hordes of weaker ones.
* HyperspaceArsenal: Generally averted, except for one peculiar instance. If a survivor drops their handgun for a melee weapon, they will produce another handgun when they are incapacitated, which disappears as soon as they are hauled back onto their feet. Same for if they grab a chainsaw and then run its fuel dry.
* IncrediblyObviousBomb: The pipe bomb is one, but with good reason - its red light and high-pitched squeal [[SchmuckBait attracts the standard infected]], making it less a question of where to throw them and more a question of ''when''.
* InstrumentOfMurder: Guitars as melee weapons. Functionally, it's roughly the same as the fire axe, though restricted to "Dark Carnival", "The Parish", and the ''[=L4D2=]'' port of "Dead Air".
* KatanasAreJustBetter: Played with. Damage-wise, Katanas in the game aren't any better than other melee weapons due to all melee weapons doing the same amount of damage to zombies. The advantages the katana has, however, is its sharpness (meaning it can cut Smoker tongues), its relatively quick swing time, and consistent wide swing letting you take care of swarms of zombies at once. The "Four Swordsmen" mutation is all about these, being the only weapon available.
* KillItWithFire: Molotov cocktails, gas cans, and incendiary ammo packs. Very useful against Tanks and Witches, as not only does it deal continuous damage until death (or until the Tank wades into a body of water), it slows them down[[note]]A Witch will only run as fast as a healthy Survivor, and a Tank slows down to an injured Survivor's pace[[/note]]. Also great against hordes, as fire kills Common Infected instantly. Additionally, burning Tanks in the finale of "Hard Rain" will eventually be extinguished by the rain, and incendiary ammo only ignites Special Infected for a limited duration (enough to kill most Special Infected, but Tanks and Witches can outlive the burning).
* LudicrousGibs: Pipe bombs, the M60 and explosive ammo produce this from common infected.
** The "Gib Fest" mutation amps it up to extremes by only having weapons that cause this. Namely, the M60. With a Magnum for when you're incapacitated or when you want a little more precision. The AWP produces the same results as a single M60 bullet.
* MacheteMayhem: One of the better melee weapons available, as it's decently fast (only slower than the Nightstick), severs limbs like no one's business, and is relatively common in the campaigns it shows up in. Now go pretend you're [[Franchise/FridayThe13th Jason Voorhees]] fighting zombies.
* MolotovCocktail: Practically a staple of the series, and essential to block off an infected access routes. Also great for chipping away at Tanks and the occasional Witch.
* MoreDakka: The mounted miniguns have been replaced with noticeably-slower single-barreled M2 machine guns, but for personal use ''The Passing'' added [[{{BFG}} the M60]], which carries 150 bullets, just one of which is enough to tear a regular zombie apart and which anything bigger doesn't last long against.
* TheMusketeer: It's possible to have a melee weapon as reserve instead of a pistol. Certain mods go even farther and give melee weapons their own unique inventory slot, allowing the survivor to carry a main gun, a sidearm ''and'' a melee weapon of their choice.
* PowerfulButInaccurate: The AK-47's main advantage compared to the other rifles is its high damage per shot; on Normal difficulty, it one-shots Common Infected. However, its accuracy is much worse, forcing you to stand still or be lucky enough to grab a laser sight if you want to reliably hit anything smaller than a Tank. This also goes for the M60, which has even more power than the AK-47 but the same accuracy.
* RangedEmergencyWeapon: Downplayed with the pistols. Despite being outclassed by primary weapons, they're rather decently accurate, damaging and fast-firing unless you're incapacitated.
* ShootingGallery: In ''Left 4 Dead 2'''s "Dark Carnival" campaign, you can stop to participate in a shooting gallery whose prize is a lawn gnome; carrying the gnome through the end of the campaign nets you an achievement.
* ShortRangeShotgun: Averted. The shotguns are a viable weapon choice, even at a reasonable distance. The Remington 870 Chrome Shotgun, in particular, has the tightest pellet spread out of all the shotguns, giving it a decently effective range, and the SPAS-12 isn't much worse.
* ShovelStrike: One of the two new weapons added in the Last Stand DLC.
* SniperRifle: A proper sniper rifle appears in addition to the Hunting Rifle from the first game. As expected, it has pinpoint accuracy when scoped in or when fired from a stationary position and deals decently high damage (enough to take out common Infected with a single hit below Expert), and also has a decent clip size, making it usable for firing into crowds at close range as well. The Last Stand update, which enables the ''Counter-Strike'' weapons for all regions, also gives access to the Steyr Scout and AWP, both of which also have excellent stopping power (with the AWP in particular having the highest damage per shot in the game), but being bolt-action rifles, both are very slow to fire, making them less efficient at close range.
* SituationalSword: Explosive and incendiary ammo's effectiveness depends heavily on what weapon you're using them with. On the one hand, using it with an SMG or M-16 greatly ups its effectiveness due to their large clip capacity letting you fire off a lot of OneHitKill bullets against Common Infected; on the other hand, it's not as great when paired with a Sniper Rifle since it was doing that already, and unlike its normal bullets, the special ammo lacks [[OneHitPolykill overpenetration]], meaning it's only helpful against Special Infected (and given that a Sniper Rifle can kill most of those with a single headshot, even that might not be the case unless you run into a Tank or Witch).
* SticksToTheBack: Every weapon and inventory item except pistols (they get holsters), pills/adrenaline, and grenades, which all go on the survivor's belt.
[[/folder]]

** It is entirely possible to counter every single Special Infected's pinning attack (Smoker's tongue, Hunter's pounce, Jockey's riding, etc) with a well placed shove, shot or slice. However, the window for you to perform these actions are measured in ''a fraction of a second'', but it feels completely awesome to do so.

* DaylightHorror: Daytime segments don't just change the lighting, but the behavior of one of the Special Infected. Witches normally sit in one place at night, but during the day they wander around.

The plot is roughly the same as the previous game: a deadly virus epidemic has claimed the country and zombies prowl the streets. You play as one of four survivors trying to use guns, swords and {{Improvised Weapon}}s to make their way though bloodthirsty hordes of mutant infected to reach safety. The difference this time is the setting, which is located somewhere around the [[DeepSouth Louisiana area]].

The lead up to the game saw much controversy after it was announced at 2009's E3 and was set to be released in November that year, a single year after the release of the first game. Unfortunately, Valve's claim at launch of the original game that they would update it following the model of ''VideoGame/TeamFortress2'' updates promptly backfired, as large numbers of people were ''outraged'' that they were expected to buy content they were under the impression they'd either get for free, or get as a mod rather than an entirely new game; this gave rise to [[http://steamcommunity.com/groups/L4D2boycott the biggest outburst]] of "ruined!" cries ever: a 40,000+ people '''boycott'''. A couple months before the sequel was due, Valve flew both leaders of the boycott to Valve's headquarters to playtest the game, where they admitted that it was "well-made". After Valve's release of a new campaign for the original, "Crash Course", and the leaders admitting that the boycott had since become just a general anti-Valve group (most members of which had [[{{Hypocrite}} bought the game they were threatening to boycott anyway]]), they decided to shut it down.

The game also received massive critical acclaim for both its MythArc style narrative - the parts of the story they don't tell you, as well as the interactions between the survivors - and for its EmergentNarrative, in which different aspects of gameplay combined with elements of randomness mean that every single time you play a new, funny story emerges.

Like the first game, Left 4 Dead 2 is effectively a love-letter to the zombie films of TheSeventies and [[TheEighties '80s]], with survivors armed to the teeth giving the Apocalypse a taste of its own medicine.

The plot is roughly the same as the previous game: a deadly virus epidemic has claimed the country and zombies prowl the streets. You play as one of four survivors trying to use guns, swords and {{Improvised Weapon}}s to make their way though bloodthirsty hordes of mutant infected to reach safety. The difference this time is the setting, which is located somewhere around the [[DeepSouth Louisiana area]].

The plot is roughly the same as the previous game: a deadly virus epidemic has claimed the country. You play as one of four survivors trying to make their way though bloodthirsty hordes of mutant infected to reach safety. The difference this time out is the setting is located somewhere around the [[DeepSouth Louisiana area]].

The game sports a few new features such as three new special infected: the self-explanatory Charger, the acid-puking Spitter, and the body-clinging Jockey. Also introduced is the new Scavenge mode, an eight-player mode similar to Versus where the point isn't to reach the safe room; it's to collect gas cans and dump them into a generator, the winner determined by which team can get more into the generator before they're overwhelmed. Also introduced is Realism, where most auras are removed (including the ones around teammates), Witches instantly '''kill''' on any difficulty except Easy, there are no "rescue" closets (dead players only respawn at the start of a new level), and a few other things. The narrative to the game has also changed as each campaign now leads into the next one rather than being standalone (for the most part) like the first game did.

** In the first map , melee weapons are available right from the start and a Magnum is set to spawn early on, giving players access to the new secondaries immediately. Additionally, bile jars very frequently spawn in hotel rooms and can be dropped by the Hazmat Infected that often show up, and the stage being set in a burning highrise means [[NewWeaponTargetRange you can make good use of them by chucking them off the building or into a fire and watching the Infected eagerly run to their deaths]]. Adrenaline shots and a defibrillator are likewise guaranteed to spawn.

** And the shove motion ''itself'' has been nerfed by making the fatigue mechanic (shove too many times without giving yourself time ot rest and the game starts applying an increasingly longer delay before you can shove again) apply to all modes rather than just Versus. This punishes the fact that you can get completely surrounded and need to shove your way out.

** In the first area, melee weapons are available right from the start and a Magnum is set to spawn early on, giving players access to the new secondaries immediately. Additionally, bile jars very frequently spawn in hotel rooms and can be dropped by the Hazmat Infected that often show up, and the stage being set in a burning building means [[NewWeaponTargetRange you can make good use of them by chucking them off the building or into a fire and watching the Infected eagerly run to their deaths]]. Adrenaline shots and a defibrillator are likewise guaranteed to spawn.
** The second area includes a gun shop that gives players a convenient way to try out any weapon in the game, including the new additions (but not the ''Counter-Strike'' weapons since those came after, though as of ''The Last Stand'' they can be found in the closet next to the stairs), and also gives access to laser sights. You also get to fight a crescendo event right after to test out your new gun.
** Because the campaign is set in broad daylight, all Witches will spawn in wandering mode, showing off their new behavior.

** Primaries; Shotguns, Automatics, and Sniper Rifles. The 2nd game includes a Light Machine Gun and a Grenade Launcher.
** Secondaries; A pistol which can be dual wielded with another. The sequel adds the Magnum Pistol and melee weapons.
** A kit-based item; The game's token Medkit. Two more items were added in the sequel: A defib and two different ammo kits.
** One grenade; Pipebomb, a Molotov Cocktail and the Bile Bomb from the sequel.
** And a temporary health item; The first game only sported Pain Pills, while the sequel added another use for the slot with Adrenaline.
* TheLoad: Competely aside from the issue of bad players, any time you engage in an EscortMission, the party is reduced to three members as the person carrying TheLoad cannot use their weapons. (Gnome Chompsky can be used [[ImprobableWeaponUser as a lethal weapon]], but it requires [[BackStab very opportune movement]], or a ''lot'' of shoves.)

* MadeOfPlasticine: Because of how melee weapons work, it's entirely possible, and really easy, to carve through a ZergRush with, let's say, a [[http://en.wikipedia.org/wiki/Baton_(law_enforcement) baton]]. Also, hitting a special infected with a [[FryingPanOfDoom frying pan]] will kill them in one hit, except for the Charger, who takes two hits, and the Witch/Tank, who are MadeOfIron.

** Occasionally, after reviving from a pinning attack (eg. Hunter's Pounce, Charger's Charge, etc), the Jockey will just flat out ignore the rule, approach you while you are getting up and ride you. Rarely the Smoker also just snares you with his tongue, though it's not as common as the Jockey situation. Chargers can also do this, though they usually turn a corner before returning to try to finish you off with a charge.

* MyRulesAreNotYourRules: AI-controlled infected can spawn anywhere, melee while stumbling, climb things player-controlled infected cannot, and AI-controlled Hunters even have a lunge move players cannot perform.

** And the shove motion ''itself'' has been nerfed with the addition of fatigue: do it too many times and there starts being a delay before you can do it again. This punishes the fact that you can get completely surrounded and need to shove your way out.

** Last Man On Earth removes all common infected... as well as the other three survivors. The only saving grace is that you'll revive automatically after being stunned to incapacitation by Hunter, Smoker, Jockey, and Charger. Otherwise... you have to repeat the stage until you give up or succeed.

** [=TAAAAAAAAAAAAAAAANNNK!!!=] plays it for fun, by removing AI-controlled special infected and having players only be survivors or Tanks. This can actually make the game much easier, as survivors can [[LeeroyJenkins just run like hell through the level]] without having to worry about being stunned by Hunter, Smoker, Jockey, or Charger. A Co-op equivalent, Tank Run was added in the Last Stand update, which removes common infected but makes every Special Infected spawn as a Tank. And they spawn on a timer, so multiple Tanks can be active at a time if you don't kill the previous one before the next shows up.

** A Spitter's spit that lands in an elevator will leave behind a much smaller pool and will fizzle out more quickly so that the survivors aren't cheap shotted when the doors are closing in.
** After the motel in the first map of Dark Carnival is a huge slope that the survivors must slide down. For that section only, fall damage is disabled so that the players don't have to worry about taking major damage from sliding down really fast or hitting the bottom by jumping.

** When playing single-player, Scavenge finales do not require you to collect all of the gas cans, to compensate for the survivor AI not being coded to do so.

*** Much as Survivor bots can't set off alarmed cars, they also cannot startle a Wandering Witch with gunfire (they can still startle her by running into her, but this is far less likely of an occurrence).

** The Chainsaw Massacre mutation amplifies the survivor bot's stupidity to new levels. They will either run ahead or lag badly behind and not do too well in saving you from special infected. This was corrected later causing the AI to rarely stray far from players, but they are still have issues, the main one being the bots' ineptitude with melee weapons.

*** A similar case also happens for Smokers. In the first game, the survivor bots would usually be really quick in saving someone caught by a Smoker. In the sequel, they now will sometimes ''wait'' until you take damage before they free you. In the worst case scenario, they'll ''sit and watch'' as the Smoker chokes you to death, not even ''bothering'' to shove the tongue off.

** If the bots get close to the safe room, they make a beeline for it and stay there regardless of the threat level in the immediate surroundings. This can lead to you getting pounded to death by a Tank and swarms of infected while the bots cower in the safe room. Doubly annoying considering that in most other situations, the bots are too dumb to keep up with you if you aren't constantly stopping and looking over your shoulder.

* LoopholeAbuse: Many achievements require specific stipulations in order to be unlocked, such as beating every campaign on Expert. The same achievements are still credited if you do them in any Mutation mode, even if said mutation makes it easier to achieve (such as Gib Fest, where all Survivors have the strongest gun in the game with unlimited ammunition).

** Survivor bots cannot set off alarmed cars, nor can they startle wandering Witches with gunfire (they can still startle one by bumping into her), preventing bouts of ArtificialStupidity related to these.

* LoopholeAbuse: Many achievements require specific stipulations in order to be unlocked, such as beating every campaign on Expert. The same achievements are still credited if you do them in any Mutation mode, even if said mutation makes it easier to achieve.

* TheyChangedItSoItSucks: InUniverse example: Coach references this with the Midnight Riders' new albums, describing them as "no good".

** The Last Man on Earth mutation alters the special infected behavior where, if you get pinned by a Smoker, Hunter, Jockey, or Charger, they will back off once they reduce your health to zero and the player the player automatically revives in black-and-white mode so that you can regain your bearings. However, this mercy is not given if you get incapacitated by any other means.

* BoomHeadshot: Played straight, to YourHeadAsplode levels with common infected is you use a caliber bigger than pistol ammo. Headshots instantly kill Common Infected and deal greatly increased damage to Specials, and on higher difficulties and Realism most Infected take reduced damage if shot in anywhere but the head. Mercilessly averted with the Tank, which takes no extra damage from headshots.

* PreviousPlayerCharacterCameo: The main draw of ''The Passing''.

* NeverSplitTheParty: The game is '''built''' on this trope. Get separated or lose track of your teammates and YouAreAlreadyDead.

** [=TAAAAAAAAAAAAAAAANNNK!!!=] plays it for fun, by removing AI-controlled special infected and having players only be survivors or Tanks. This can actually make the game much easier, as survivors can [[LeeroyJenkins just run like hell through the level]] without having to worry about being stunned by Hunter, Smoker, Jockey, or Charger.

* UniqueEnemy: Each campaign in [=L4D2=] has an "Uncommon Infected" unique to it:

** The M60 machine gun fires bullets that shred infected, much like the mounted guns: its shots will gib common infected in one shot and pass through multiple bodies. Its high damage per shot, fairly rapid fire, and ammo capacity of 150 rounds will allow a player to fairly easily mow down an entire horde or tackle a Tank on their own. Its main drawback is that you cannot refill its ammo at all (not even with special ammo pickups) and you only get one full box. And once you run out, you automatically discard it, leaving you with only your secondary weapon unless a new primary happens to be on hand. In official campaigns, it only spawn randomly in The Passing (the update that introduces the weapon), Cold Stream, and a guaranteed one in The Last Stand.

* DeusAxMachina: Fire axes are understandably a fairly common melee weapon, given that you're trudging through the remnants of civilization. They have a fairly slow swing rate, but the widest range in the game, making them excellent for chopping down hordes.

** The second area includes a gun shop that gives players a convenient way to try out any weapon in the game, including the new additions (but not the ''Counter-Strike'' weapons since those came after), and also gives access to laser sights. You also get to fight a crescendo event right after to test out your new gun.

** Melee weapon damage to Tanks has been nerfed. Damage is now 5% per hit instead of 10%, which means now that survivors will most likely have to resort to kiting now instead of everyone running up to a Tank and smashing him with four Frying Pans Of Doom.

* RandomlyDrops: Hazmat uncommons (Dead Center and the Sacrifice) with bile jars, riot cop uncommons (the Parish) with tonfas, and fallen survivors (the Passing) with random items.

** A few specials can cause this singlehandedly: Tanks (natch), Chargers, and (if your team is [[TooDumbToLive spectacularly incompetent]]) Hunters.

* WeCannotGoOnWithoutYou: If there are any bots on the team in any non-Versus mode, you'll have to start the level all over again if all the human players are dead, regardless of if there is a bot player alive. It becomes mind-boggling when playing against a team of bot Survivors in versus mode and they are capable of moving through the level on their own without the guidance of a human player. Fortunately, there are {{Game Mod}}s that fix this.

* AKA47: As with the second game, though a few guns, both old and new, are now referred to by their real names.

* LudicrousGibs

** Infected players can manually trigger this when they are at a certain distance behind the survivors, allowing them to skip the respawn time that would happen if they jumped off a cliff instead.

** The minigun and mounted M2 machine gun, which can shred oncoming hordes and Tanks, are never positioned so they can effectively cover more than two of the generally five or so directions that zombies can come from in official maps. They'll also overheat after about fifteen seconds of continuous firing, rendering them unusable for an entire minute. Additionally, the M2 is rare in comparison to the previous game's minigun, only showing up in two finales out of six.

* KatanasAreJustBetter: Played with. Damage-wise, Katanas in the game aren't any better than other melee weapons due to all melee weapons doing the same amount of damage to zombies. The advantages the katana has, however, is its sharpness, its relatively quick swing time, and consistent wide swing letting you take care of swarms of zombies at once. The "Four Swordsmen" mutation is all about these, being the only weapon available.