Massive Skin Thief
A massive Skin Thief, ogre sized. Able to use magic, including showing the ability to warp healing magics, and can wear multiple skins. Escaped by flying away on a pair of wings hidden underneath a skin. Accused you of working with “The One That Bring Pain”.
According to Pimply, Nurgle apparently felt the compulsion the Skin Thieves experienced stronger than all the others, and served as an organizing force. You have speculated that this closer connection to whatever force is behind the compulsion is why he is different than most of the other Skin Thieves. You have not ruled out some other explanation, however, as The Builder (who has apparently been hired by the King to eliminate the Skin Thieves) has indicated that they are evolving in response to experience and outside stimulation.
You have run across him a number of times, most recently in the Slag, deep in the Underbelly, where he blocked your escape, but otherwise only watched as his minions futilely attacked you.