Finally, something other than infantry.
I envisioned him as formally a Dreadnought in the service of the Death Guard before they fell. Once the Horus Heresy hit, he was infected with some type of malediction and began the rise (or fall?) to daemonhood. He's retained what was once his Dreadnought powerfist as his main weapon, the rest of the hull splitting and rotting off as he turned. I'll probably use it as a counts as Black Mace.
He's turning out very fun to paint, just gotta add in a few more washes and get the white to stand out a little more on his fist. I like his shiny little bug eyes, gives him a very creepy look!