A building made out of living flesh and steel- the moving is an afterthought, the leftover legs simply placed beneath it and colectively being strong enoguh to barely sort-of carry it. It is not a formless evil creature like a baneghoul- Although their flesh is fused and grotesquely distorted, each human is still there, still concious, individual and perhaps even sane, each ones features fairly easily discerned and identified.
Tunnelling through the moving mass of meat, sort of reminiscent of a hobbit hole in architectural style but larger and lots more evil, is an extremely opulent villa. Grown mainly from living bone, every millimetre masterfully engraved by black imps, decorated with the most decadent gems and furs, no comfort missing- an impressive place. A place of indugence and gluttony unimaginable.
On the very top of the tower is an enormus throne, made from the very most sensitive parts of each victim and making them howl in agony at the smallest motion of the one sitting in it, and constantly compelled to squirm in humiliation. A squirning that through thoughtful placement of the right organs is made to function as a convenient and pleasant massage mechanism. This throne is very much a command centre, and hooked up to inumerables enchantments concerning communication and charisma. It is a place to command armies from, to watch out over seas of peons bowing beneath you, to work spells over vast distances from, to meet diplomats upon, and many other things.
Finally, the defining feture of the entire structure, permeating it everywhere, is a vast instrment. A pipe organ, to be exact, and setting upon the throne among gadgets the most striking thing will be not the many mgical gadgets, but the rows upon rows of keys. Each key connects to the mind of one man or woman who have wronged you, inducing not only excruciating pain, but also an immeasurable sense of doom and sorrow. Their screams of agony, tuned to perfect pitch by masterwork pipes yet leaving their unmistakable fingerprint in the timbre, combined into music of unearthly beauty, consists powerful magic indeed. It's true potential, however, is it's combination with demon tungue, using the same method as
http://www.youtube.com/watch?v=muCPjK4nGY4 , and interweaving with more traditional powerfull enchantments of domination and charm. And it does require skill, at both demontungue and music, to use. With that, however, few things can hold a similar sway over minds in precision, width, power, or mass application.
Technical note:
Due to the quirks of arcane ritual magic, the people making up the organ pipes are in fact first made into cat people, and the boundary between the mechanical and biomagical parts of the mechanism consists of a nail striking their tails. And that's it's gameplay effect: other than being a fancy chair and a glorified tent, it provides whole-battlefield buffs and debufs in the style of the titaneghouls shriek, but more powerful and with the ability to coonvey any emotion or even commands or anything else we could by personally speaking to a single person in demontungue.
We can make this the next time we have several hundred prisoners to torture or kill which couldn't just be made into peons, ones that are still enemies, ones that needs to be punished. And lots and lots of resources and magic since it's a rediculusly large project.