I was managing a decent fortress, so far with 70+ dwarves and very good exports, when all of a sudden...
The dead walk!I had a small military, which after locking down my 2-level airlock, dispatched the necromancer and the swarm of zombies while only sustaining one loss. A tomb was constructed, and all was well. Until of course, a goblin ambush appeared.
After having such success with my crossbowmen in the last siege, I decided they would make short work of a small siege, and let them loose without thinking to lock down my fortress. This was a dumb idea, because a single goblin managed to kill my entire 15 dwarf military by itself, and made it inside, killing several children before it was slain by a dwarf with a pickaxe.
I was picking up the pieces after that, and managed to clean up some of the bloodbath, when I noticed that all of my dwarves were incredibly unhappy. Not wanting a tantrum spiral to occur, I started trying to make the dwarves happier. Before I had a chance, I noticed that a trail of blood was forming inside my fort. After looking at the unit list for a surviving enemy, I noticed one anomaly: "Kivish Sakzulibesh Mozir Unib, Woodworker"
I drafted an emergency military out of miners, but by then it was too late. He had already slaughtered my entire fort's population of children, and elevated himself to Legendary status. He then proceeded to disembowel every last one my my fort's 59 remaining dwarves. I've never lost a fort so quickly before. I managed to send a Demigod adventurer to the site afterword, with whom I disarmed Kivish by slashing at his hand, then stabbed him in the chest, and while he was impaled, I bashed his skull in with my shield. I seriously love this game D:
I couldn't get a pic of the bloodbath in time before it quit, but here's a pic of the outside, with the woodworker's body.