Dark Mechanicum
When Horus, Primarch of the XVI Legion initiated the events of the Horus Heresy, a vast amount of the Mechanicum sided with the Warmaster. Promising Fabricator General Kelbor Hal with the key to the Hidden Vaults of Moravec on Mars in exchange for the support of the Mechanicum, Horus not only gained a powerful ally, but unleashed the dark desires of those Tech-Priests that felt hindered by the laws of the traditional Mechanicum. Dark Mechanicus technology is heavily intertwined with the Warp and have no boundaries when it comes to genetic experimentation and advanced cybernetics that push the limit of Humanity. The results are horrifying hybrids of fused flesh, forbidden technology and the ungodly touch of Chaos.