Yeah, the thralls and husks are easily terrifying. I think in the original thread where they were discovered, he unleashed hfs on a large battalion of them. thralls tied hfs, only because the map was covered by webs. search for voidbreach. Other fun things are the eternal resurections, and, uh one more thing, oh yeah, blood rain. So many new horrifying things are here. And MINECARTS. oh yeah, now zombies in resurecting biomes are immortal. Cut them up, they collapse, then their constituent parts ressurect. People have seen skin come back.
EDIT: I found the post with giirlinhats explanation. She sums the thralls up well:
Thralls are living creatures, minus everything that makes them a creature. They are alive, they are not undead, they are truly living creatures, except all the things that distinguish a creature from a corpse, they lack. They feel no pain, they do not breathe, nor bleed, nor tire, nor thirst, nor hunger, feel no pain or sorry, no joy and take no pleasure even in such things as mist. They suffer no order and no chaos. They are, truly, neither alive nor dear, nor really undead. A Husk is, at its core, a void. A sin against god in the purest form. Not simply a blight like a dwarven fort will be named "a sin against nature" but in every sense of the word the Husk is a sin, something which defies nature and embodies everything that should never be.
A Husk will never breath, eat, rest, or suffer fear. They make an ultimate killing force which simply cannot be stopped.
A Husk ignored all orders, they will not don armor nor remove it, and cannot be controlled except by extremely physical means of walls and locked doors.
A Husk is NOT undead. It is not a zombie. It still counts as a living creature, and as such will eventually age and die - perhaps the only true way to defeat a Husk is simply to wall them off behind the bowels of the mountain and try your best to forget that they sit there staring at the wall and craving your death. Never stopping, never tiring, never becoming distracted, the Husk has one, single, universally persistent thought - to kill that which lives and remove life from the world. Even as they sit sealed behind the walls, they only linger there. Only a layer of piled rubble and their forgotten ability to remove constructions keeps you safe as they spend decades, centuries, screaming thoughts through their (possibly torn) brains of all the ways in which they would end your life.
A Husk is not something to weaponize. Not yet. Nothing short of bringing the mountain down atop their heads will stop a Husk. They need no lungs, no limbs, they don't even need a brain. Reduced to a bleeding, fractured torso they will crawl forward, possessed of otherworldly hatred and fueled by the purest of rage, these beings of raw terror will gladly and effortlessly bring the largest of dwarven mountainhomes to a smear of dust in the time that it takes them to crawl from one end of the entrance to the lower part of the forges.
Perhaps one day we'll be able to utilize them. They are something of raw power, and we are not ready for that quite yet. Dwarves who harness the power of magma and upheave heaven and earth itself falter at the strength and single-minded purpose of the Husk. We are not ready. Dare I say it but... we are not depraved enough, not ingenious enough, not brave enough to rally the Husk.
This being of unadulterated terror remains the only thing that the craziest of dwarves will avoid.