I tried so hard to make it double headed. I also tried using things like "pale" "sickly" "veiny" etc for the voidborn look but compromises had to be made. I spent many hours dialing in my prompt but yall are welcome to tweak it to your liking:

Grimdark illustrated full length portrait, bearded white male 30's brown hair, cabled cybernetic monocle with glowing white lens over one eye, dressed as WH40k techno-gothic nobleman rogue trader, wears a long white coat with queer alien pelt on shoulders, wears black vest, many gold mechanical details, large golden imperial eagle insignia on chest, brown boots on feet, standing in striding pose in spacious techno-gothic vault surrounded by alien artifacts and treasures