So, a Forgotten Beast shows up, made of filth and with deadly spittle, but he can't get through the walls surrounding my farms in the caverns. He wanders off, but I try to keep a close eye on the Units screen for his eventual reappearance. Two seasons pass, and I gradually check the unit screen less and less until I no longer check it at all. At this point, I've got a dozen dwarves running into the caverns in a bucket brigade to fill a bathhouse inside of my fortress with water from the underground lake there, with water coming into my walled-off region via a channel.
"Urist McBucketBrigade cancels Fill Pond: Interrupted by Forgotten Beast"
With the floodgate open, the FB had run up the channel and emerged in my farming area. I quickly mobilize my military, sending them down the main stairway as chaos breaks out, with the Beast chasing dwarves to and fro, spitting frozen globs of extract and generally making a nuisance of himself before chasing one of the dwarves up the main stairwell into the fort proper.
Where he is intercepted by a pair of hammerdwarves.
They begin pounding on him with their silver warhammers, blocking each spit attack with their shields until the steel-clad sworddwarves show up. Meanwhile, my marksdwarves, who have until now insisted on bludgeoning every single enemy, sit 2-3 flights up the stairway, raining bronze bolts of death on their enemy for the first time ever. Several minutes of frantic battling ensue, until finally, the first dwarf to intercept him cuts the beast in half.
With his hammer.Seeing extract and blood on the stairs, I immediately restrict all traffic to those tiles and designate constructed stairs to be built over them. My masons clean up the mess within minutes, while my now-inactive soldiers duck into the new bathhouse, all traces of the beast rinsed off in the water that other idle dwarves soon clean up and haulers dump the "filth" that was left behind in lieu of a corpse. Soon, no absolutely no traces of the creature remain. No casualties and, one season later, still no syndromes.
So yeah. I feel pretty awesome right now. Can't wait for my first DF2010 siege