No Mercy/Walkthrough

No Mercy can be played on any difficulty level except for Easy. It is the only heist where the amount and locations of security cameras are dynamic, with the former being scaled according to the number of human players present at the beginning of the heist.

Tactics

• If you intend to go through with Plan A, then carry a silenced weapon or be prepared to use a melee attack on the cameras.
• Because of the very close range and hectic pace of the heist, the best primary weapons to carry are those with great damage per second, such as the Brenner 21 and AK.
• The GL40 and Mark 11 are often useful because of how tightly the enemies are clustered, especially the GL40, which can easily eliminate Shields in a narrow corridor. However, players should be wary that the GL40 can easily cause accidental civilian casualties.
• Don't kill any civilians; they have heartbeat sensors that will trigger the alarm if a heart stops.
• Don't go near the ICU after you've drawn your weapons; otherwise, somebody will see you and trigger the alarm.
• Hospital staff are more likely to get up and trigger the alarm.
• The best strategy for keeping the panic buttons untouched is to have one player guard each of the three buttons and shout constantly, while the fourth player completes all of the objectives.
• After a certain amount of time, the wall in the room opposite the elevator will be blown open. A path between the elevator and the laundry room may also be opened. You can use these to more easily navigate through the hospital and complete objectives.

Walkthrough

Plan A

If you fail plan A then plan B will start.

Go to the reception desk and search for cameras. There will be three cameras for each human player present at the beginning of the heist, up to a maximum of 9 cameras (the amount of cameras scales with the number of human players) The cameras are located around the reception, north corridor, main corridor and in the adjacent rooms. After you've found every camera, position yourself so every player can cover a button, destroy their fair share of cameras and start the heist. You must destroy every camera with your silenced weapons (B9-S or Mark 11) or melee attacks within seven seconds; otherwise, the alarm will go off.

After the cameras are destroyed, every player needs to cover their respective button so that no civilians trigger the alarm. The three panic buttons are always located under the reception desk, in the north corridor and in the elevator room. 

Your next objective is the computer; interact with its keyboard to find the patient you're looking for in the computer. It is advised that you have the fourth player not covering a button do this along with finding the patient file, because it's possible for a civilian to trigger the alarm while your back is turned. The hospital management will periodically call about problems with the camera; simply interact with the phone so that Bain can handle the call. After you've been instructed, search for the patient files and check every file you find by holding F (default) while looking at it. There are quite a few patient files, some of which are almost invisible, but they are mostly in the reception room; the others are in the adjacent rooms. The location of the correct patient file is randomized.

Make sure you keep all of the civilians down. By now, a guard or repairman could be coming up the stairs next to the spawn area in order to check the camera malfunction after the phone call. The guard must be quickly killed with a silenced weapon, and the repairman should be taken hostage (you can kill him, but you'd incur the 10-second penalty). It sometimes happens that Bain does not alert the crew of the repairman coming up, most likely when he is in a phone call. However, if he does not give you further objective instructions/reminders, there is a high chance that the repairman will appear. It can also happen that a civilian will come up the elevator, this lets off the distinctive elevator "ding"-sound, it's best though to check the elevator and stairs periodically. You should always have a spare cable tie left in case the civilian appears, because he is very close to the alarm button.

After you find the patient's file, you must set up four fake sentry guns to suppress the civilians. This will no longer spawn any guards or civilians, so you don't have to worry about the reception area anymore. Then, go into the changing room and don surgical scrubs by walking into the orange area. You are now back in stealth mode.

Go into the ICU and talk to Doctor Eriksson by standing near her. Follow her and listen to what she says. She will make two rounds for you to determine which patient is the correct one. He will not be responding well to treatment and will not be released soon. He is also often suffering from "an unknown disease", rabies, an abnormal heart rate, or abnormal blood pressure levels. Sometimes, she will mention that the patient is suffering from "Green Flu". After you've determined the correct patient, memorize the color of the wire connected to that patient's chamber; it will either be red, yellow or blue. Follow the wire until you reach the alarm box.

Start the heist and interact with the correct wire to cut it. If you fail to cut the wire in time or fire an unsilenced weapon before the wire is cut, then all the shutters will close and you will be forced to use the saw. After cutting the wire, go back to the hallway (don't be afraid to shoot the guards as the alarm is already triggered) and break the glass of the chamber whose shutter is still open. Read further at "After Plan A or B."

Plan B

If you trigger the alarm prematurely or cut the wrong wire, then you must obtain the saw inside the stuffed cow (which will be highlighted) and use it to cut the ICU door open. Then, saw one of the three chambers open. When you're done sawing one chamber, break the glass and check if you can take blood samples from the patient. If not, repeat with the next chamber until you find the correct patient.

After Plan A or B

If you've found the right patient, then you can take blood samples from him. These samples must be verified by one of the seven validation devices, five of which are scattered between the reception desk and the elevator and two located in the north corridor. If a device is provided an invalid sample, then it will destroy the sample and clean itself. You can run all of the devices simultaneously.

After one blood sample is successfully validated, call the elevator in the ICU; it will be outlined in orange. Continue checking blood samples until you obtain another valid one. Each human player can only carry one valid and one unverified blood sample, so if playing solo, you must leave one valid sample in the device. Any blood samples, valid or unvalidated, has a chance to be dropped and destroyed if you are downed by anything other than a Cloaker's melee attack. Alternatively, you can leave all valid samples in the validation devices so that you risk having the vials destroyed only after the elevator has arrived. One way that not many people know is if you are crouched when you go down, you will not break the vial, so if you have a vial in your possession, it is best you stay crouched until the elevator's arrival. Granted, there have also been reports of crouched players losing their vials when falling into bleedout mode, so this is not a surefire way of avoiding it.

While the elevator is descending to floor 4, you must restore the electricity and then recall the elevator a few times.  Activating the power within 5 second of it being shut down on Hard or above also yields the achievement "Afraid of the Dark." When the elevator doors open, place the two valid blood samples into the test tube holder, and start the elevator when all of the crew members are inside.

Pick up the crowbar in the corner of the elevator if you do not already have one. During the ride, the lights will flicker and the elevator will shake as a result of the army firing missiles at the hospital. At this time, beware of Cloakers who may break through the ceiling and attack.

There are two different endings:

1. The elevator stops at floor 33, where there is an inferno that sometimes has two Bulldozers. Use the crowbar to break the floor, then descend the revealed ladder and run to the orange escape zone, where Bain will be waiting.
2. The elevator plummets down to the ground floor, and every NPC will fall to the ground after the elevator stops. You can tell this will happen if the display showing the current floor goes off. Use the crowbar to open the elevator hatch on the floor, crouch through it, and break the elevator door. Run through the morgue until you reach an emergency car. You will be unable to avoid taking fall damage when you break out of the elevator and if your health is too low, you may be downed from the fall damage. It is possible for the crew to be doomed to fail if all crew members are extremely low on health.

There is always escape time 1:05 regardless of difficulty. 

• Bill (Left 4 Dead)
• Lucky camera placement
• Alarm button
• Take extra cable ties

1/4

• The elevators
• Intruder #1
• Intruder #2
• One of them

1/4

• The alarm box
• The patient
• A validation device
• The patient

1/4

• The darkness
• Power box
• The cooler
• BBQ

1/4