I've heard of this game. Seems pretty cool.
I remember one of my towns (I like building above ground) got over run by goblins, when I ran out of military, and forced my civilians to mob the invaders. They all died. This was after managing to strike the second cavern, and spotting to fbs wandering around in it. I decided to reclaim, because it was the best fort I ever had on that world. Once my dwarfs showed up, I discovered that the goblins that murdered me were still there, chilling around the streets, not doing anything. Weird, I thought. I immediately set my dwarves to collect the previous loot.
I was surprised when I discovered the giant, flying leech had made it through the wall by the caverns, and was sitting in a pond on the surface. The goblins nearby immediately sprang into action, attemtpting to kill the thing, but all eventually dying. During the battle, another dwarf stumbled upon the giant, one eyed toad was waiting in my mine, like a bad man in a swivel chair, facing a wall. He chased that dwarf around for a while, and more goblin allies arrived at the scene. In a matter of minutes, both beasts had ruined my attempt to reclaim, and most of the goblins, too. I was hilarious to watch them all running.