So I've played for a few years now, on and off. I can get to a point where my forts can get fairly comfortable until they inevitably die from slowdown. So I say, "tyrman, my lad, it's time to embark to an evil biome!"
Yeah. Some kind of murky rain fell on my dorfs immediately, started melting them, and then... then the zombified ravens came. Chillingly, they pecked out the eyes first
So I picked a new embark, 4x4. Half of it was a savage woodland, the other a terrifying evil biome to the north. I feverishly brought everything down a z-level once I spotted the horde of a dozen or so bloodthirsty owlman corpses. My dorfs gripped their weapons grimly and I waited for... ...
Huh, where are those owlmen anyway?

Turns out they'd spotted a Giant Sponge. And they hated it. The whole horde just settled on it, beating the crap out of the giant sponge. It took about a year for my fort to get almost walled off, unfortunately due to a pesky aquifer that took forever to slip through. I was in the process of finishing the last bit (the roof) when undead keamen descended on my lone (priceless, doomed) woodcutter, killed him, and then took off with all of his clothing. His body got hit with an evil cloud, zombified, and got in the fort. Then it was the typical downward spiral from there, culminating in almost all of the undead getting walled off in a side channel before someone's severed zombie head gnoshed my last dorf to death.
And, as he lay bleeding out on the ground, the giant sponge was still getting thrashed into unconsciousness by those owlmen. Thank you, nameless Giant Sponge, for keeping me alive for a year. You win MVP of the fortress Netstraps.