4th Fel Prefects

The Fel Dynasty, like all dynasties, had house troops. With how deep the Dynasty was in the Cold Trade, their house troops because expert combatants.
They were hardened on a dozen worlds, battling in Leman Russes bought quietly from many locations. Perhaps they were exposed to dark powers in one of their engagements or found too many relics in the trade. Or mayhaps the tanks themselves were tainted.
When they found their master was slain, they went mad. Something snapped and they attacked blindly before lifting to an unknown location. They formed some sort of pact with hereteks to resupply them. More and more of their gear seemed to come from the Screaming Vortex.
However, resupply seems to be an issue. Many repairs seem hodgepodge or rely on the unusual binding of minor demons. One of the most common seems to be the use of lost souls of the insufficiently devout as engines.
Their loyalty seems to be to no particular Chaos god.

4th Fel Prefects

The Fortunous Dynasty's Exploits Redrick