Lost my fortress to a animated yak hair.
I settled my necromancer adventurer in the fortress and then reclaimed it. The first year was good, but then he found butcher's workshop. All the fortress(about 50 beards) gathered around this terrible hair zombie, unable to land a hit, each of their attacks passing right through. During next 3 months they passed out from exhaustion, one after another, only to continue the fight after they regain conciousness, eventually dying of thirst and hunger.
Well, tecnically necromancer was still "alive" and kicking. Kicking the hair non-stop. After one more month of this, I abandoned the fortress.
May be, it's worth mentioning, that the necromancer cheated himself about hundred kills. He was constantly raising a zombie, killing it, and reanimating a corpse again.