I would've posted this a bit earlier, but my OS spontaneously chose to ignore the existence of my network card.
Have you considered lever-operated menacing spikes to kill the FB? Build the corridor of death, lure it with dogs or cats - when pathing into the kill-zone raise bridges to trap the beast - then pull lever in repeat mode. Voila, you now have swiss-FB-cheese without dwarven casualties
That sums up Plan A...
Trow him some useless animals to give him a reason to use his dust, he will die soon.
...and that Plan B. Both didn't work.
The upright spears trap with an artifact grate I used to kill demons is still there, however Sostet went towards the floor hatches I installed above the forges in order to be able to isolate them in case of danger, passing near a bunch of giant sloth bears and dingos left there.
Thanks to the fact that the dust syndrome wasn't immediately fatal like Radavi's, they dealt some damage to it before death. Much, if not most of the blood visible on the screenshot belongs to the FB. While it was heading deeper, I decided to set up the bait to lure it towards the upright spears. The trap would've had to suffice - the enormous range of the dust cloud (while fighting animals on the stairs, it managed to reach up to 8 z-levels higher than the source) meant the beast would've been able to attack the marksdwarves on the fortifications above should I decide to send them there. This is probably how the demon-slaying marksdwarf Litast I mentioned before perished - her body was found on the stairs leading there.
All this left Sostet quite heavily wounded:
Yes, this is a lung and heart indicated as non-functional. Despite this, it kept crawling around for weeks.
But before I could let the dwarves herd the animals near the trap, I had to close a gap in the wall I deconstructed to retrieve a dead baby's skeleton. Using the gap and ignoring all orders the new captain of the guard, Kivish Shegetavuz, went down to get himself some gear and stumbled upon the beast in the forges. Having no weapon skill and only partial armour didn't stop him from slaying it - but not before painting a considerable part of the floor with its blood. He expired some time after that, of course. His sacrifice will not be forgotten.
After resuming the normal activity in the fortress, I noticed that a dwarf is carrying somebody familiar to the hospital. As Oiledring, the axedwarf from the previous update. He survived two months in the caverns, unconscious, rotting and starving, only to ultimately starve in the hospital just when I finally got somebody to fetch him some food. Maybe that's better? He lost his eyesight, was rotting, and a large chunk of his body had been melted away previously.
After these events, six soldiers were all that was left of my military. Fortunately, migrants with military skills started to arrive, and a macedwarf and an axedwarf were drafted. Still, that's eight. Barely enough to defend the surface. For this reason Wirejade is turning towards automated defence. I'm launching a research project with the aim of developing simple, effective, easily replicable and adaptable weapons using impulse ramps. The testing range is being prepared in the northern part of the fortress aboveground, and I hope to post the results soon, here or in a separate thread. Hmm, maybe some more artifact-based spear traps? I need to look around for good locations.
Occasionally, dwarves still bleed out and fall dead. Inspection of the clothing doesn't reveal any forgotten beast extract coatings on the clothes or the body. Majority of those incidents has taken place in the main dining room, an area far away from any possible dust residue. I commissioned 90 pairs of leather shoes, hoping to prevent further deaths, if stepping in it is the cause.