Hello, I made with the tips for the quest in the description and the gameplay showcasing the pain of it. The tips follows.
Go to the lighthouse (the landmark) entrance in the lighthouse map. It is located in the south west corner, by the beach. You need to enter the area where the invisible sniper scav (the same one that shoots you when you cross the map border in woods by the car extract and customs by the stronghold train track). You will need to run until you get face to face with the vehicle. The sniper scav will aggro on you and actively shoot you in the leg, thus blacking the leg out and damaging your stamina. For this you will need a painkiller, I'd recommend a propital (so you can run with the blacked leg and restore some health while running) and most likely an SJ6 to counter the stamina damage. The sniper scav will stop shooting at you after you get far away enough, he will miss some bullets but he will land every bullet in the same leg. Cover doesn't help, he will bypass it.
