This started out as a normal embark; I decided to try creating a bunch of self-sufficient farmer/brewer rooms, with minecarts to feed the main fortress. That's not super important, though.
The fortress was going wonderful for quite a while (though I had been neglecting booze, and didn't have very much of it), and then an elf caravan showed up. I was about to send a bunch of dorfs to the trade depot with a bunch of crafts when I got a message:
The forest titan Bebmal Náshaslenod Sezomâst has come! A huge feathered spider. It has a fat, bulging trunk and it has a regal bearing. Beware its poisonous bite!
I hadn't trained any military dwarves at this point, but I figured that the elves would take it out no problem, so I just ordered my dwarves to hide for a bit. To my surprise, the titan just moved to the entrance to my fort and sat there. It wasn't long before I was deciding whether or not to go and try to lure it onto the minecart track so I could hit it with a few high-speed death machines, but just then I got another message:
A vile force of darkness has arrived!
I thought, "Oh, the goblins can take out the titan for me!" However, they attacked the elves, and then got the titan's attention. It killed them all without injury.
At this point I decided to lure the titan onto the track. I sent a single dwarf, and it went and killed him - 1 hit with its webs was enough. The titan then continued to sit at the entrance. Neither did a 40 dorf assault do anything, even moving it from its post.
A bright point came when some migrants showed up. They led the titan away from the door, allowing me a moment to brick it up. But the dwarves all went to drink, and got slaughtered. It wasn't long before the only two living dwarves were a couple who fell down some stairs and had their spines broken.
Fortunately, some migrants arrived and were able to collapse the ceiling on Bebmal's head.
Now to bury 120 dwarves...