Obtainable starting early in the second mission, this achievement is not hard but requires minor setup. Find a guard who is not moving around, preferably with a nice space behind him/her. Use Foresight to look around and go behind them, making sure you are facing their back (if you're facing the wrong way it won't work) and put a Displace marker behind them (not too close or they'll explode, which does unlock the
instead).
Once the marker is set, turn off Foresight then walk into the open so that you are line-of-sight to your marker. Trigger displace and immediately attack. If you set it up right you'll do a quick instakill and unlock the achievement.