On HUNTER killed the nosalises before they break through the vents
Metro 2033 Redux QUICK DRAW – Achievement / Trophy Guide
At the end of the Chapter Hunter you will have to defend your position from Nosalises breaking into 4 ventilation grilles. Once you have the revolver, ignore the monsters coming from the ceiling and focus on the grilles. The Nosalises will go down with one shot. To make this easier, turn on the hitmarker in the option to see when you got one and move on to the next vent. Shoot quick and check all 4 vents constantly. It also helps to watch where your teammates are shooting if you can’t find the next monsters.
Instantly reload the checkpoint if you see that a vent is open. You will start directly at the beginning of the break in.