

Take out the Cyst in the corner with a green crate. Ignore the exit and keep walking until you see 2x lockers, a green crate and 2x ammunition. Move on and kill the Cyst above the exit with an explosive barrel. Next to 3x lockers, a green crate and 2x ammunition is a Cyst attached to a wall. Step out of the elevator, move clockwise and watch out for Cysts.

Stay in the middle of the elevator cabin. A few hints: it's faster to look around with, then quickly aim instead of aiming down the sights while waiting for Tripods. If the achievement didn’t pop, reload your last save and try again. Revert back to the save you made before investing everything into the Pulse Rifle and continue.
