Wight

The wight is a horrendous form of aberration created by the warlock spell "Core of Annihilation", which sucks the souls forcibly from the body of a living humanoid and replaces it with the dread silence of the Void. The awful potency of the primordial blackness suffuses the body of the now deceased creature, twisting whatever tiny remnants of spirit still remain within its material vessel into sheer insanity.
If a wight's warlock creator lives, it is compelled to faithfully serve its master with the loyalty of one who has no-one else to turn to in the hateful world of creation. If the warlock is destroyed, the wight loses its only hope of returning to the timeless silence from which it was spawned, and resorts to the immediate slaughter of any form of life it comes across. While at this point it is analogous in both appearance and behaviour to a zombie, its terrifying strength and core of darkness make it unimaginably more powerful a threat.
From the darkest corners of the world it comes staggering forth at alarming speed, its warped and twisted limbs snapping the force of its unnatural movements but never hindering its advance. Once it draws near, its hollow eye sockets become apparent, as well as the dreadful blackness which lies behind them - the demon which infests the cadaver and wishes only to quash the living. As it descends upon its hapless victims and proceeds to tear them violently limb from limb, its mouth opens in an empty scream, the dissonant and horrified cry of a being of nothingness trapped within a plane of agony-inducing matter.
The manner in which a person's soul is cruelly wrenched from flesh and replaced with perverse darkness by the Core of Annihilation rite is actually very similar to the Song of Annihilation performed for a prospective warlock by a demonic voivode, although the victim is without the long period of conditioning and systemic corruption which allows the strong-willed cultist to withstand the transmogrification whilst retaining some measure of cognitive integrity.