Just met my first Forgotten Beast, it came from the caves and soon made its way to my stairs as my guys were putting up the last block of fortification. I try to mobilize my squad when I realise that somehow it got erased since last save and some of my guys, despite being alive, cannot be picked to get back into the squad, very odd.
So I draft a whole new group of people, a couple with skills they already brought with them. A particularly unhappy dwarf who just got the news about the draft barely got time to get suited up before she went downstairs before the rest of the squad was ready to join her. The beast had luckily not made it's way up the stairs, having deciding on chasing a kid down the caves. When it became disinterested in the kid, it turned over to my new recruit, fuming with rage at the beast who had disturbed her daily routine of constantly hoping to finally be asked to milk something.
Os, the Forgotten Beast didn't seem to stand a chance, for the poor quadruped... ahem... made of snow... got the shit punched out of it like a snowman getting ravaged by a bully. She simply punched two of its feet off followed by a complete leg, single-handedly slicing the upper body off its torso.
The rest of the squad then showed up wondering why she was standing in puddle of slush and what the hell this whole alarm was about. That night, she would tell tales of her grand battle against Os, the Forgotten Snow Beast, but her comrades would only politely nod and joke about it with her, not believing an ounce of it as she had nothing to show for it at all.
Yeah... so no loot on that beast