Haha, congrats, hope you took joy in the slaughter. Do you mind if I also share something on this topic?
I just lost a thriving fortress completely in one swoop the first time ever since picking up DF (I guess I play cautiously) to a forgotten beast. An undulating mahogany pigeon, beware its poisonous sting. I was working on a construction project in the caverns, and stupidly had left the wall to my fortress temporarily open.
A pigeon? I thought, this can't be too bad, we've killed tons of forgotten beasts already after all, even ones with worse things than toxic stings. But this thing gave me all of three seconds of warning before swooping across the map into my main stairway like an X-wing into the Death Star's trench, like "well surely I can at least wall over the main stairs or the - IT IS ALREADY AT THE FORGES OH GOD". I think it killed, envenomed or disabled 40 dwarves before my military even got there, which was followed by one desperate season of them pounding on it with their pathetic copper to imported steel axes, not even making a dent, and their dying one by one, more getting drafted and the fortress crumbling slowly but surely. I even bought animals from the elves to release to fight it in desperation, tried to cave in parts of the fortress on it, but no, it's still there flying manically around and my fortress is not. Went to visit it in adventure mode and it caught my superelvenly agile demigod like a bolt of lightning would a cheetah. I've never seen anything move so fast in the entire game.
Well, I was impressed. I like to think of it as a small mahogany hi-tech hunter-killer robot sent to decimate my fortress.