Didn't realize my parent civ was dead
Built a fort to accommodate 200 dwarves, but I only ended up with 16, 3 years in and haven't got a migration wave since first 2,
My two miners froze to death in a mining accident, my moat froze, and I was using it as a chance to fix some issues with it, and a pocket of water washed over them and froze.
Then after that I had a little leak issue, I already had my indoor waterfall / water supply for hospital up and running, was digging a tunnel under my moat, and didn't realize there was a hole at the bottom of a part of the river a little deeper than the rest and it flooded my fort, 9 dwarves trapped in their room, 3 trapped in the greathall, but I was able to rescue them and build walls to stop the flooding from destroying everything.
I just lost access to the housing complex, and the metal working area. over 100 bars of steel, and a bunch of iron and gold, a few hundred charcoal, I'm planning on doing a rescue mission to get it all back and reposition it.
and gonna wait until next winter and hope it all freezes over, but I'm not thinking it will, if it does I can dig out all the ice and move it somewhere else.
Just had an invasion, I installed a mod to make invasions more deadly / more often, was some random 4 armed monkey race, 19 of them riding giant jaguars, but was able to stop them with just 4 warriors in full steel armor / steel spears/swords.