HAHAHAHAHAHA! Oh heavens, this is just hilarious. I manage to seal Stosbub in the old, mostly unused part of my fortress, which only contained six smoothed bedrooms my only still (a horrible oversight, on my part) and a craftsman's workshop. Oh, and several of my humans, too. Of particular note was the bone doctor mother of an infant and a child. She was in her bed when the beast attacked, and she and her baby were ripped apart. The child survived, however, and is trapped in the empty level between Stosbub and the shaft leading down through the caverns (though the shaft at the second cavern is submerged in 7/7 water due to a failed attempt at dousing a layer of semi-molten rock). There was one other living person trapped on the layer with the little girl -- a female human planter named Use Fordworship. She heroically built a wall to keep Stosbub from escaping to the caverns below (I had been planning on using a cave-in to kill Stosbub, but I ultimately deemed it too risky for any of my three legendary miners). For her act of selfless heroism, I gave her the custom profession name "She Gave her Life to Stop Stosbub". However, shortly after this was finished, I received a visit from Aca Ithacavere Lima Mima (Aca Sheenknights the Sport of Coloring), a female cyclops. HAHAHAHA! Is that not hilarious?!
But I think I'll see what I can do, because win or lose, it's still Fun as hell, doncha'know.
[EDIT:] When I looked at the unit screen to find out where the cyclops had gone, I noticed that Stosbub wasn't there. Curious, I investigated. You know what I found? Stosbu's rotting corpse. It was killed by a woodburner punching it in the head, bruising the brain through the skull. Of course, the wood burner died as well, but seeing "Stosbu Diedseas the Fiend of Lakes (I guess it must've gotten the name when I wasn't looking). d. 253" on the kill list of one Cuthroz Wumuthalo "Cuthroz Paddedscaled", Wood Burner, made my day. According to his profile his physical traits are described as "He is very strong." Well, I should certainly think so, considering he punched out a MOTHERFUCKING forgotten beast. I think that, if nothing else, this fortress was worth it just for this.
(I don't care if Stosbu was already pretty much dead on its feet when it got here, it was still awesome.)