This is for those people who are confused on WTF this map is doing. Im going to list the gimmicks of this from the probable first encountered to the last.
-"Hurry" Hordes: Happens after some time has passed after a: the start of the map, or b: last hurry horde. Hope you either got peirce or full-auto when it comes because it will spell your doom if you back yourself into a corner. They are also on full sprint. They also dont give points.
- Car Alarms: "Watch your fire!"-Bill. Be careful around any car, if you hear it's turn signals. DO NOT SHOOT THE CAR. If you do, you summon a horde on you. Good news, it give points. Bad news, it takes ammo.
- Multiple Perk Locations: You may be curious if you can get quick revive after you go off the Apartment. Or Speed Cola after starting the Generator Room Crecendo Event. You can.
- Cresendo Events: Basically, horde events but in a confined area. They happen for any loud or bright reason, like the Gas Station Cresendo or the Rooftop Finale (more on that later). Once you start the cresendo, the way back is usually locked or non-viable.
- Threat Zones, the Witch and the Tank.: Basically spawns for the Witch and the Tank. There is a chance for 1 of 3 things to happen; either the zone is not used, a Witch is spawned, or a Tank is spawned. Witches are basically proximity mines that chase you if you startle them (shoot them, get too close, have your flashlight on them for too long, be close for too long), and will not stop until they down/kill the target, which then they will run away. If you have a shotgun, turn your flashlight off, aim at the back or head and blast her. Going prone and ADS at her head or back helps you, in the L4D community, Cr0wn her. Tanks do what the name says; soak up a lot of damage and dish out a lot. Good news, the shotguns always get a full hit because of the bulky frame. Bad news, it takes less damage to shotgun. Your best bet is to get either a full-auto or high-damage weapon, probably a gun that does both, like the M60.
- Finale: Cresendo Event but 3 times as deadly (three Tanks) but much more open. The Rooftop is where you start a radiowave frequency with the heli pilot to tell him to come over and help (he gets bit trying to street-pickup some survivors en-route) and then survive against a massive horde that follows a 5-wave formula. First wave is just alot of Commons. Second is a tank. Third is first but with more Commons. Fourth is a tank. When you reach wave 5, the rescue vehicle (the News 5 Chopper) arrives and you are prompted to enter it to escape. at wave 5, the Tanks and hordes come at the same time, incentivising you to get to the rescue vehicle.