Crescendo Event

"Get ready ladies! Here they come!"

- Francis

"This is why we have guns!"

- Nick

Crescendo Events are actions that cause a massive onslaught of Common Infected, often called a Horde, to find and attack the Survivors. The cause is often a part of the environment that the Survivors must activate in order to progress through a level, generally acting as mini-finales. An important factor during game play is that Special Infected (including Tanks) are invariably intermingled or interspersed with Common Infected during Crescendo Events.

Most Crescendo Events involve causing a loud noise to sound or a bright light to activate, which attracts the Infected.

Another type of Crescendo Event is known as a Gauntlet Crescendo Event where rather than wait out a horde, the horde is spawning and the Survivors must keep moving in order to survive, usually to turn off whatever is attracting the horde. These types of events are only found in Left 4 Dead 2. Examples of Gauntlet Events include the Crescendo Events of The Streets, The Mall, The Fairgrounds and The Coaster, among others.

No Mercy

 * After exiting The Subway rails in the second level, Survivors have to activate a loud electrical generator to open a metal hangar door, which will alert the infected. They will start coming from the second level of the room, through the hole in the floor inside the small locker room, and from the entrance door.
 * This can be avoided by using a boost to reach the second level of the generator room. This can be achieved either by jumping on the heads of Common Infected or by receiving a grenade boost from a teammate.
 * To perform a grenade boost, one player with a grenade (Pipe Bomb, Molotov or Bile Bomb) crouches and throws their grenade straight up as another player jumps over them. The jumping player is hit by the grenade and launched into the air. Many times, it is also possible to use a Grenade Launcher to boost in a similar manner, thought Grenade Launcher boosts launch player much higher, which may cause too much fall damage in certain situations.


 * In The Sewer level, Survivors must activate a noisy lift to cross a roof and enter a warehouse. Infected pour over the metal roof and across the street below, climbing eighteen-wheelers parked below and the ladder up the lift to reach them.
 * This can be avoided by using a grenade boost to reach the roof of the warehouse, or by destroying the sliding metal door on the left side of the loading dock in Left 4 Dead 2. The door can be destroyed with a direct hit from a Grenade Launcher or several hits from melee weapons.


 * Later, in The Hospital, Survivors must use an elevator. Pressing the button causes its noisy descent, which in turn summons a horde from the surrounding walls and hallways, some even pouring in from the vents above their heads. The horde will keep coming until the elevator arrives. On occasion, the director sends forth a final horde when the elevator arrives. It is up to the players to decide whether to deal with this final horde or to simply rush in the elevator and skip it.


 * Reaching the Rooftop Finale, Survivors hear a voice from over a radio, which they use to call for a helicopter. Summoning rescue also triggers a horde event. They must survive several hordes of Infected as the pilot makes his way to the landing pad nearby.

Crash Course

 * In The Alleys, the Survivors encounter a bridge blocked by a military barricade, and must fire a Howitzer to destroy it. The resulting noise attracts a massive horde of Infected.


 * In The Truck Depot Finale, the Survivors reach a vehicle lift, with an armor plated truck at the top. They must then lower the truck with an unreliable generator that must be restarted twice. Halfway through, the power goes out, and the Survivors must fight by the light of their flashlights until the power reactivates. Soon, the truck lowers, and the Survivors board, setting off for what is presumably the beginning of Death Toll.

Death Toll

 * While scouring The Drains, the Survivors reach a flood control room. They must trigger a flood gate to drop to proceed further. The noise of the gate dropping summons a horde from the sewers below.
 * This event can be avoided by using a Pipe Bomb or Bile Bomb to gather a crowd of infected in the middle of the flood control room. The player can jump on the heads of these infected from a nearby metal platform, and use the extra height provided by the infected to reach a sewer pipe, from which the player can reach the second level of the control room on the other side of the floodgate.


 * When Survivors reach the safe house at the end of The Church level, a mysterious man known only as "Church Guy" (so called from the name of his sound file) is already inside. When you ask the Church Guy to open the door, he refuses to do it, and instead rings the church bells, telling the Survivors to "prove their humanity." The bells summon the horde to attack.


 * After leaving an office building, Survivors are confronted with a forklift holding up a cement walkway in The Town. Triggering the forklift to drop its load allows them to proceed, but when the load drops, the vibration sets off a car alarm, summoning a horde. In Left 4 Dead 2, the event is slightly different: instead of a car alarm, the forklift now has its own alarm that activates when it is used. This alarm summons a horde to attack the Survivors, and it operates as a Gauntlet Crescendo Event that lasts until they get to the safe room.
 * There is a truck to the right of the store that survivors pass through near the beginning of the level. Jumping on Common Infected or using a grenade boost to get over this truck will allow Survivors to reach an area that is past the crescendo event, allowing them to proceed to the safe room without activating it.


 * Now at the Boathouse Finale, the Survivors discover a radio. When they call for rescue, a man named John Slater answers their calls by informing them that a boat is arriving to rescue them. They must survive an onslaught of Infected, then make a break for the docks just outside of the boathouse.

Dead Air

 * Upon exiting an apartment complex, the Survivors encounter The Crane from which a dumpster is suspended. They must lower the dumpster to proceed to the next rooftop. The loud noise the dumpster makes during its descent attracts a horde.
 * It is possible to jump from the top of the fence next to the crane to the next rooftop without lowering the dumpster. This requires the player to be moving faster than normal run speed, though, so either hops or, in Left 4 Dead 2, an adrenaline shot must be used to make the jump.
 * To increase your speed with hops, the player must run forward, jump, let go of the forward button ('w' by default), then strafe to one side (either 'a' or 'd' by default) while turning their camera in the direction they are strafing, then jump again immediately after hitting the ground (timing is very precise). To travel in a straight line, players typically alternating strafing left and moving the camera left before strafing right and moving the camera right after they jump, switching sides each time they hit the ground.
 * To progress through The Construction Site, Survivors must shoot a bundle of five gas cans tied together to destroy a wooden barricade. Doing so causes the barricade to burn slowly at first, but suddenly a nearby generator explodes, summoning a horde. The Survivors cannot continue until the gas bomb is done burning, which takes about three times longer than a regular gas can takes to burn.
 * Players can bypass this by jumping on the heads of common infected to boost themselves over the barricade.
 * In order to proceed through the baggage handling area of The Terminal, Survivors must crash a van through a locked gate. This difficult horde event will yield Infected from the offices behind, over an adjacent pile of rubble blocking another hall, and the escalators below.
 * Exiting from the waiting area to the Runway Finale, Survivors discover a military plane with a pilot inside. The pilot informs them that the aircraft needs fuel, and instructs them to activate a fuel pump. Once filled, the plane can carry them to safety. However, the noise the pump makes attracts several waves of the Infected, which the Survivors have no choice but to endure if they are to escape.

Blood Harvest

 * During The Tunnel, Survivors must leave a train shed through an emergency exit, which, once triggered, sets off an alarm, calling forth a horde.


 * During The Bridge, Survivors encounter a freight train with a lever that they must pull to disengage the brake, causing it to roll backwards and knock down a bridge. Doing so allows access to the safe house at the end of the level, but the collision summons waves of Infected. In Left 4 Dead 2, this becomes a gauntlet event.
 * This can be bypassed by using a grenade boost to reach the cliff that the bridge provides access to.


 * During the Farmhouse Finale, the Survivors have to cross through a tall corn field to reach the farm. Crows living in the field are startled by the Survivors' movement, causing them to make a lot of noise, which attracts the horde's attention.
 * This Crescendo Event is unusual because the Survivors do not activate anything deliberately.
 * This event's unusual placement just before the finale, as well as the relative lack of warning related to this event, is likely to compensate for The Train Station's lack of a Crescendo Event.
 * In Left 4 Dead 2, this event is now a Gauntlet Crescendo Event that goes on until the Survivors reach the farmhouse.


 * After reaching their holdout in the Farmhouse Finale, a radio on the table in the abandoned house is used to summon a military armored personnel carrier. In doing so, the team also alerts a horde. They must hold off the horde until the vehicle arrives, which they enter from an open hatch in the back.

The Sacrifice

 * At The Docks, the Survivors must open the door to a train car with a Tank in it. The Tank's loud roars will then cause a horde to attack.


 * Like in Farmhouse Finale, the Survivors accidentally startle a flock of crows while climbing to the top of a gravel mound in The Barge. The birds' loud crowing attracts a horde.
 * This can be avoided by jumping on the partially sunken truck below the gravel mound. An invisible wall blocks players from standing on it, but it is possible to hang from the ledge of this invisible wall and have a teammate help you up to get onto the ship.


 * In the Port Finale, starting any of the three generators causes a horde to attack, and later, a Tank. All three must be turned on to lower the bridge and reach safety.
 * This finale can be avoided by standing on the fence below the mounted gun on the bridge, jumping on the head of a Common Infected to reach the balcony of the bar, then jumping from there to the platform with the mounted gun. From there, proceed to the back of the bridge with the button to raise the bridge. Jump onto the edge of the wooden barrier just to the right of the button, and jump straight up on that edge so that the game registers the event being complete and the survivors being on the bridge. From there, press the button to activate the final stage of the event, and Zoey jumps off the bridge to 'restart' the generator as normal.

The Last Stand
In The Last Stand, activating a generator causes the horde to attack. It seems that the generator's sounds and the light at the top of the lighthouse are enough to attract a very large amount of Infected. While not technically a Crescendo, Gauntlet Crescendo or Panic Event, it is the act in-game that begins a round of Survival on The Last Stand.

Left 4 Dead 2
In Left 4 Dead 2, the strategies for dealing with Crescendo Events are different, as they are more difficult to deal with. A common tactic in Left 4 Dead ' s Crescendo Events was to sit in a corner and wait it out, making them fairly easy. However, in the sequel, after the Survivors start a Crescendo Event, there will often be a second event to turn off the trigger of the horde and stop the hordes of Infected. Sometimes, it is necessary to flip the second switch to proceed, while other times, it is not actually necessary to stop the horde, but typically preferable. There are also Panic Events that occur much more frequently than Crescendo Events; an extreme example of this is the Impound Lot from The Parish's third chapter, The Cemetery.

Dead Center

 * On The Hotel, the Survivors have to ride an elevator to the ground floor, but the ride is abruptly halted when smoke from the hotel reaches the elevator. The doors must be noisily pried open to progress further, which, naturally, the horde does not take too kindly to.
 * On earlier versions of the game, it is possible to activate the elevator as you jump into the path of the closing elevator doors. You will be able to jump on top of the elevator, then jump to the next elevator car over and reach the first floor without prying open the elevator doors.
 * It is also possible to skip directly from the beginning to the end of the level. There are two methods to do this.
 * One player hangs from the ledge outside the room with the map, the first room on the right after leaving the starting room. Another player kills them with friendly fire. A third with a defibrillator begins reviving the dead player immediately, as their body falls to the floor below. The Survivor then revives on the floor below, which happens to be the lobby of the Hotel where the safe room is.
 * One player jumps from the same ledge without hanging off of it. The other three stay on the stairs immediately past the starting rooftop. Just before the jumping player reaches the ground, all three other players 'take a break' and allow AI to take control of their survivors. The AI teleport to the falling player in the lobby of the hotel. The player that jumps will die, but the Survivors who successfully teleport will be able to reach the safe room. Note that at least one player must retake control of their Survivor before the jumping Survivor hits the ground and dies, or else the level will restart because no human-controlled Survivors are still alive.


 * On The Streets, the Survivors pass through a gun shop owned by a man named Whitaker. Whitaker has barricaded himself on his roof, but now he needs some cola. There is a gas truck that is blocking the team from reaching Liberty Mall, but Whitaker has the firepower to blow it up for you. Whitaker makes a deal with the Survivors: retrieve some cola from the nearby Save 4 Less convenience store for him, and he'll blow up the truck and clear the way. The store, however, is armed with an alarm, and the resulting event lasts until you get back to Whitaker's gun shop and give him his cola through a slot in the door he is hiding behind.


 * On The Mall, after traversing through the back rooms of Liberty Mall, the Survivors must either break through the glass windows of a toy store or open an emergency exit door (whichever path the AI Director fancies for the players) to progress. This event goes until you go all the way up to the third floor's security room and deactivate the alarm. This event does not have to be stopped to proceed, although it is definitely preferred to do so before continuing.


 * On the Atrium Finale, the Survivors take an elevator down to the atrium area. While they are inside of it, they plan to take Jimmy Gibbs Junior's race car, fuel it up (as Ellis points out that cars aren't fueled for car shows), and escape the mall. Upon the elevator opening, the finale begins.

The Passing

 * On The Riverbank, the Survivors come across a wedding, where there is a Witch who was apparently to be the bride just before turning infected. Walking to the nearby speaker and turning on the music will play the Midnight Riders song "Save Me Some Sugar (This Won't Take Long)", which will then startle her and lead her to attack whoever turned it on. If the Witch is startled in any way, including the speaker, this causes a mini Crescendo Event, leading to all of the Infected wedding guests to attack you. This Crescendo Event is entirely avoidable so long as caution is exercised.
 * On The Underground, the Survivors have to open a gate, which starts a Gauntlet Crescendo. From here, they must run to the safe room through a dark sewer, constantly slowed down by the water.
 * On The Port, the Survivors have to gas up a generator so that they can lower the bridge, get back to Jimmy Gibbs Junior's car, and drive off to continue their journey to New Orleans.
 * This finale is unique, as the team is helped by the Left 4 Dead team (minus Bill) who can cover them with gunfire and throw items down to the Left 4 Dead 2 Survivors while they're busy fighting to survive.
 * It is possible to use a grenade jump to reach and walk along an invisible ceiling above the bridge, then jump down and reach Jimmy Gibbs' stock car. The fall will kill the Survivor, but so long as the other survivors are already incapacitated or dead, the campaign will still technically be completed.

Dark Carnival

 * On The Fair Grounds, the Survivors must activate a Merry-go-Round to progress. The ride attracts a wave of infected that will spawn in kind until the team shuts the ride down.
 * On The Coaster, Survivors have to activate the roller coaster to open a gate onto the Screaming Oak, attracting the horde until the coaster is shut down.
 * It is possible to climb on the support trusses holding the rollercoaster up to bypass opening the gate and summoning the infected.
 * On The Barns, to enter the stadium, the Survivors must open the turnstile gates, which angers the infected and causes a massive horde that will spawn until reaching the end of the level.
 * It is possible to get over the fence in front of the stadium and reach the safe room very early in the level. After leaving the building with the bumper cars, use a grenade jump to get on the top of the tall fence in front of the gap in the hedges. Walk off the edge of the fence just as you get shot with a grenade launcher, causing you to hang on the edge of the fence.
 * On The Concert Finale, the Survivors must activate the lights and fireworks of the Midnight Riders' abandoned concert stage to signal to a helicopter to evacuate them from Whispering Oaks. The ensuing music and pyrotechnics show attracts the horde.

Swamp Fever

 * In Plank Country, the Survivors must call a small ferry for them to pass through the swamp; However, it will produce a loud noise which will attract a large horde towards them.
 * Sometimes, this event can be skipped completely by using the nearby Jukebox to play Jonathan Coulton's "Re: Your Brains," a song that attracts the horde, then heading to the Gator Farm to activate the ferry.
 * On older versions of the game, it is possible to use a propane tank to initiate a stumble glitch across the swamp without calling the ferry. First, set the propane tank down on one bank, stand close to it with your back facing the other side of the swamp, and set it off. You will stumble. Switch weapons very quickly to 'break free' from the bank of the swamp, then switch weapons periodically to restart the stumble animation. You will progress backwards as you stumble, floating over the water until you reach the other side.
 * In The Swamp, the Survivors encounter a wrecked airliner, and are forced to open an emergency door to pass through, sounding an alarm.
 * In older versions of the game, it is possible to use adrenaline to jump from a rock on the left side of the plane to the top of the plane, reaching the other side without opening the emergency door.
 * In The Shantytown, a loud, rusty ramp must be moved to get to a shack above, creating a loud, Horde-attracting grind.
 * In the final chapter, The Plantation, the Survivors send a radio call to Virgil, captain of the Lagniappe, and request rescue. They then hold out in a plantation house, in a way similar to the original Left 4 Dead Boathouse Finale.

Hard Rain

 * In The Sugar Mill, the Survivors need to reach the sugar mill below from the third story of a building, but a very loud elevator is the only way they're going to actually be able to go safely. Naturally, the horde is not pleased.
 * It is possible to use a Propane Tank to jump down from the building without dying. Throw the Propane Tank down to the ground, then jump on top of it and set it off when you are close to it. You will stumble in mid air, negating your momentum.
 * In Mill Escape onwards, weather effects are now active. Rain is falling at this point in the campaign. Every time there is a flash of lightning, you have been signaled that a massive downpour is about to occur, which will then attract a horde.
 * The finale takes place in the middle of a monsoon on top of a Burger Tank restaurant, where the Burger Tank sign must be activated to flag down Virgil and his boat. The light from the sign attracts the attention of the Infected in the area.

The Parish

 * In The Park, the Survivors find a CEDA trailer. As evidenced by a sign inside of the trailer, opening up the door, exiting the trailer and breaking the threshold of the street will activate a very loud alarm, which will summon an endless wave of Infected, until the Survivors reach a tower with the alarm switch.
 * In the 3rd chapter, The Cemetery, the Survivors emerge from a manhole into an impound lot filled with alarmed cars. This appears to be a potential "slippery slope", in that setting off one alarm will likely cause many more of them to be set off by stray gunshots from the ensuing battle. (Considered an "optional crescendo event" instead of a series of panic events.)
 * Near the end of The Quarter, the Survivors have reached a hotel complex. The Survivors must get across a gap between the roof of a pool house and the balcony of another, so they use a conveniently-placed parade float to bridge the gap. The Survivors will be attacked by infected until the float crashes.
 * It is possible to reach the balcony without activating the float in three ways.
 * Jump from the balcony of the previous house down to the sloped roof of the house below, bunny hopping off of it to gain significant speed and reach the next belcony.
 * Stand on the concrete cinder blocks below the balcony and jump on the heads of common infected to receive a boost.
 * Use a grenade boost from the same area.
 * In the finale of The Bridge, the Survivors must lower a two-story bridge to cross the bridge and escape New Orleans on a military helicopter that is waiting on a helipad near the end of the bridge. After the bridge is lowered, the heavy metal gate locks up for a second, slamming harshly into the ground. The sounds of an entire two-story bridge lowering and a metal gate crashing onto the ground end up being the metaphorical "starting guns" for the race between the Survivors and the Infected.

Panic Event
Unlike Crescendo Events, Panic Events are things that can be avoided as the Survivors proceed through a level, if they are careful. There are five different things that can trigger a panic event. The number of summoned Infected appears to have been tweaked by recent updates.

Alarms
"You have GOT to be kidding me!"

- Nick

Cars are strewn about the map in virtually every level. While most are harmless, you'll occasionally find an alarmed one. These can be easily identified with a reflective red glare on the car windows. When shots are fired near an alarmed car, it will send out a short "beep", warning trigger-happy players to watch their fire. If an alarmed car is hit or touched, it will set off an alarm that send a horde at the team.

For obvious gameplay reasons, the Infected cannot directly set off car alarms. However, they can still indirectly set them off:


 * A Smoker can drag a Survivor towards an alarmed car, setting it off.
 * Indirect explosions (you can avoid by firing at long range):
 * A Boomer that dies near an alarmed car
 * Explosive rounds (Left 4 Dead 2 only)
 * Explosive objects (Gas Cans, Oxygen Tanks, Pipe Bombs)
 * Being punched by a Tank into a nearby alarmed car, which will set off the alarm. If the Tank directly attacks the car (by punching or throwing a rock), the alarm is instantly disabled; it will not go off.
 * Chargers can pummel Survivors into an alarmed car (knocked Survivors can also set off an alarmed car if they land near/on it)
 * Jockeys can steer Survivors into alarmed cars.

Car alarms will not go off if a shot lands from long range. In Left 4 Dead 2, Incendiary ammo can also be used, as incendiary shots will not trigger car alarms. Car alarms are rather rare in Left 4 Dead 2, with the exception of The Cemetery, where the Survivors have to pass through a parking lot that is literally full of alarmed cars.

Metal Detectors
In The Terminal level of Dead Air, the Survivors approach the security area. As with any airport's security area, Metro International Airport has metal detectors. Walking through one of them will trigger the noisy alarm (and the Panic Event), as the Survivors are clearly carrying quite a lot of weaponry and ammunition made of metal, However, they can simply walk around the two functional detectors and avoid the event completely. Pulling the Survivors through metal detectors is a popular tactic for players that are using the Smoker in Versus.

In Left 4 Dead 2, the level was changed. This time, the team must go through the metal detectors, causing a Gauntlet Crescendo Event to occur instead. This was probably to make the level more difficult.

Boomer Bile
Survivors hit by Boomer bile will be blinded, and one horde (in addition to nearby Infected) will specifically target biled Survivors. Bile bombs are similar to Boomer bile, except they work on the Infected instead. Regardless, once the bile wears off, the Infected present in the area will attack the closest Survivor to them.

Time
After a certain period of time, the Director will send a horde at the team. The time it takes for the Director to summon and send a horde varies by difficulty. The Director can also send a horde if the team backtracks, though the difficulty still influences how fast they will spawn. The only exception seems to be Dead Center's third level, The Mall, where hordes come very quickly regardless of difficulty but come with fewer Infected to compensate for it.