Perform the Serpent's Fury 3 times.
This trophy is missable. Serpent's Fury is a purchasable skill from the green Skill tree. You must first buy "Serpent's Strike" (1 skill point) and then "Serpent's Fury" (2 skill points).
To perform this move you must stealth kill two enemies standing next to each other. Perform this on 3 pairs of enemies and farm it via checkpoint restarts.