Enslaver

Overview
Enslavers are enigmatic entities which emerged from the Warp shortly after the War in Heaven between the Old Ones and the C'tan. Due to the impossible levels of death and destruction wrought throughout the war, the Realm of Souls was corrupted into the Warp and the Enslavers crossed over into the material universe. The Old Ones, near extinction and exhausted from fighting the C'tan and Necrons, were unprepared for the Enslavers and were effectively wiped out, along with every other species they had created, save for the Eldar, Jokaero, Hrud and Krorks. Eventually, after scouring the Milky Way galaxy clean of most of its resident life, the Enslavers disappeared, either returning to the Warp or simply starving to death. Over eons, the galaxy gradually recovered and the few who are old enough to remember the Enslavers believe them to be gone for good.

In the 41st Millennium, the Enslavers returned and infested the Calixis Sector, but were promptly exterminated by Human forces. Strangely, these Enslavers were far weaker than the original infestation.

Biology
Despite originating from the Immaterium, Enslavers seem very different from Daemons and other entities of the Warp. As they predate the Chaos Gods, they are not allied with the ruinous powers and are seemingly driven to feed on anything and everything. Also unlike Daemons, Enslavers leave behind a corpse upon death rather than evaporate back into the Warp.

In terms of physiology, Enslavers resemble bloated, oversized ticks or fleas with tentacles, relying on telekinetic levitation for mobility. Enslavers feed on the souls of other lifeforms and are particularly drawn to Psykers when hunting. To feed, Enslavers penetrate the victim's brain with their tentacles and drain their soul through them, whilst simultaneously turning them into a mindless husk under the Enslaver's control. Once the slave is of no further use, the Enslaver will implant its eggs into their head, which will explode upon the eggs hatching. It remains unknown whether or not Enslavers are sapient or driven by instinct.