Possess every type of possessable enemy.
This achievement requires you to play as Paxton Fettel (Story) or a Wraith (Soul King). You can possess most types of enemies in the game, you can't possess Powered Armor or Monstrosities. Possess all possible enemy types to earn this achievement.

ATC Soldiers - Generic enemy you mostly kill, comes with various weapons. You must possess one of each weapon type (SMG, Shotgun, G3A3). Found in various Intervals and Soul King.
ATC Sniper - Covered in an urban ghillie suit, wields the sniper rifle. These are only found in Interval 04 and 05 and Soul King.
Phase Caster - Regular sized ATC with a blue phase shield, summons ATC enemies. To be able to possess the Phase Caster, you must destroy his shield. Play the Campaign in Intervals 02, 05 and 06.
Phase Commando - Large sized ATC with blue phase shield, teleports through walls. To be able to possess the Phase Commando, you must destroy his shield. Play the Campaign in Intervals 05 and 07.
Psycho Melee - Civilian enemy, attacks with crude weapons or hands. You must possess one of each weapon type (Hands, Axe, Pipe, Wrench, Crowbar). Found in Intervals 03 and 05 and Soul King.
Psycho Ranged - Civilian enemy, attacks with throwing knives. Must play the Campaign, found in Interval 03.
Psycho Suicide - Civilian enemy, wears an explosive vest. Must play the Campaign, found in Intervals 03 and 05.