I had a Beast show up just yesterday and it finally found a way into the Fortress (my fault, I kept digging down looking for magma and broke into it's cavern).
This is the first time I have ever had one GET into my Fortress.
The Forgotten Beast Amomu Cewi Covace. It was a huge scaly mite, with a pair of knobby antennae, a body that "undulates rhythmically" and it had gray scales which were jagged and close-set. Oh, and deadly spittle. Sounds dangerous but when it attacked some citizens, a Fishermen Dwarf acting like a miner and his kid, they escaped totally untouched.
When my warrior Dwarfs attacked it the thing went down like a chopped down tree. A few Dwarfs had some light wounds and it turned out the "deadly" spittle was frozen acid which the warriors would either dodge or just knock out of the air, like the stuff was snowballs or something. A Hammerdwarf was credited with the kill and I give it the nickname 'BeastKiller'. Now I have two Dwarfs with nicknames (the other was credited for killing a Minotaur).
To be honest I was kind of surprised. It is one thing for my Dwarfs to swarm and kill a Minotaur or to kill a small group of Goblins but I thought a Forgotten Beast would put up more of a fight.
One poor Dwarf was selected to carry the body all the way back to the surface to be dumped. I think he gave up at one point (to go drink or eat or something...Guild rules you know) and somebody else took over.
Kind of sad...we never think of the aftermath and the poor, poor Dwarfs who have to clean up the mess.
The cavern has been sealed up, though I did put a door in the walls, so I can access it again if need be. Dogs, doors, and traps fill the tunnels to it, so I will be alerted if anything else tries to break in.
I assume Forgotten Beasts are not always so.....disappointing? They don't even make engravings about the event!
Funny enough, after this I found warm stone. After carefully digging about, like I was playing mine sweeper, I found the magma and set up my first magma forge of the Fortress. And only the second one I have ever set up (the first was a failed Fortress I put in the side of a volcano).
I am kind of excited about that.