As I type this my current fort is paused and I just made a backup of the save so I can try and figure out what just happened after I watch what is going to likely be the fall of this fort. Or at the very least a painful memory.
It is the 5th year at Shedimkatdir, or "Shadowglimmered", and the Dwarven caravan is unloading at the Depot while my dwarves bring the mass of worn clothing, rusty armor, and various trinkets I had nearby. Things have been going smoothly from the start, with only two early casualties when a Hunter, and baby, tried to wrestle with a few Drakes. The metal industry has been going good, the military is full of killing machines, and there are even a few new recruits working on some mage training. Besides a recent stone shortage, and related stone journal overflow (How do we have 500 journals? What do you mean we never set the workflow limit?), everything has been going great.
At least until right now...
I'm not even sure what exactly happened, but after a quick screen jump to see my military cut a kobold in two, I jumped back to the Depot to do some trading. That's when I see the entire Depot area filled with deadly poison. As the smoke clears I start looking for combat reports, or anything, that might tell me what happened. Nothing. All I have to work with are half of my dwarves, possibly more, and all of the traders/guards on the ground unconscious, suffocating, and in extreme pain.
I'm not sure why they would have gone off, but the only thing I can think of causing this are the few stacks of Manticore ammo I set to be brought to the Depot.
So now I'm gonna watch as half my fort suffocates. On the bright side, none of my military and even the Baron were elsewhere in the fort. 60 of my 123 dwarves were nearby though, so this should be interesting...