The Corpus Mymir was a device utilized by both Loyalist and Traitor Mechanicum forces during the later years of the Horus Heresy.
One among many of the innovations of Zhao-Arkhad that saw that Forge World's censure by the orthodox Mechanicum authorities of Mars, the Corpus Mymir is a psychically active servo-skull. Contained within the drone, the brain of a psyker is kept at a basic level of activity through a combination of drugs and electro-charge implants, allowing it to maintain some basic telepathic and divinatory functions.
Before the removal and implantation of the brain, the donor, who was often forcibly selected from the highly psychically active population of the moons of Zhao-Arkhad, receives extensive mimetic conditioning and hypno-therapy, fixating it upon a simple auto-suggestive phrase. Repetition of this phrase by an authorised operator triggers the subconscious manifestation of simple psychic phenomena by the servo-skull.
The fact that these devices, often prone to catastrophic failure, became commonplace on the battlefields of the southern Imperium during the savage inter-Forge wars of the late Horus Heresy speaks as much of the desperation of the combatants as it does to the efficacy of the weapon.
History
A vast panoply of the arcane exists within the galaxy, spread far and wide on the worlds and in the fleets of Mankind and the Outsider. Attempting to apply a classification or category based on a single shared property of all of these relics, tangible and intangible, is a nigh-on impossible task, for they are myriad in form and use. The term 'psyarkana' is used in lieu of such a classification, and is considered to be a catch-all term to refer to ill-understandable and ill-definable items or practices, often of ancient or mysterious provenance. Broadly though, psyarkana fall into two groups: techno-arcana and esoterica.
Techno-arcana are usually strange relics and devices based upon what can be loosely understood to function through technological and scientific means, though rarely can these means be reproduced. Such items, be they human or xenos in origin, are recovered from lost civilisations, discovered in the darkest reaches of space or, under the rarest circumstances, created by the artifices of the Imperium. They can be potent archaeotech stamped from those STCs which survived the Age of Strife or alien artifices which predate the evolution of Mankind entirely. Esoterica, however, often refers to intangible rituals, practices and powers as found in ancient manuscripts which are not easily understood. Often these are wielded through psychic or arcane means, and are suggested to interact in some respect with the currents of the Warp, though this is not confirmed to be true in all cases. Whatever the truth behind such arcane articles, all produce effects contrary to our grasp of the order of nature.
Many arcane technologies and strange devices were recovered during the Great Crusade, both relics of Mankind's lost endeavours from the Dark Age of Technology and the product of alien minds and cultures now lost to history. Of these relics few now remain, most were destroyed by the Legiones Astartes as they advanced across the galaxy, deemed too dangerous or profane to remain in human hands. However, some yet survive, either taken as trophies or consigned to the vaults of the Legions or the laboratories of the Mechanicum. In particular, the Iron Hands and their master, Ferrus Manus, proved prolific in their acquisition and subsequent interment of powerful and dangerous relics, a number of which would reemerge after their keeper's death.
During the Horus Heresy, desperation led many to wield psyarkana they little understood or could scarcely control. Those organisations previously forbidden from making use of dangerous techno-arcana, particularly amongst the Mechanicum and Iron Hands Legion, would continue to covet these strange technologies. Those who had once searched for proscribed esoterica, experimenting with their knowledge in secret would go on to openly embrace it. Many would wage their own campaigns contrary to the orders of both the Warmaster and the Emperor to take possession of psyarkana at the height of the Age of Darkness. The use of these psyarkana relics carried with it the risk of terrible consequence, or else irrevocably tainted the user. Regardless, such rituals and devices were sought after by every faction of the Horus Heresy and frequently changed ownership; pried from the lifeless hands of the vanquished.
Sources
- The Horus Heresy - Book Eight: Malevolence (Forge World Series) by Neil Wylie and Anuj Malhotra, pp. 300,303