See, here's your problem. Never engage them directly! Use spear traps, spider and regular traps, marksdwarfs, mine cart shotguns and maybe even other forgotten beasts! Guile is always the preferable option.
Agreed! Especially because in this case I had even tested my "lock down the caverns" lever to see if it worked. It did, so I could have just ignored that thing and dug around the issue. But I just had to say "fuck it" and go full dumbass instead.
It was fun, though. I had the best combat animation I've ever seen in the game, when there was a fight between my militia commander and this thing next to a magma forge. It turned out to be a building destroyer, so it wrecked the forge before charging my militia commander, who promptly dodged into the newly created hole and fell, while I had him on "Follow," down into the magma and then sunk down every layer before dying.
I realized at that point my "fuck it we can take this thing" estimate of the situation was overly optimistic.
I know there are smarter ways of doing this and until recently, I've been absurdly cautious, but dying in some ridiculous catastrophe is more fun than dying of FPS which is just depressing, especially when it's otherwise an interesting fort. The embark is also incredibly rich in all forms of coal, has every single iron ore, and flux, and I just found a relatively generous vein of adamantine, so I just decided at the outset that "maniacally aggressive almost without reason" was going to be the strategy and the fact that we'll all be kitted out with adamantine soon has increased my resolve in that department.
(I will take a little more care that my champions don't go diving in magma again, though. Losing adamantine weapons that way is painful.)