My most recent badass was 'promoted' to get him out of his other jobs, in which he was performing slowly and spending more time in the tavern than the workshops.
He picked up an iron spear and suddenly had a purpose. I never did catch him training, but apparently every time he got sent to kill something or stumbled across something hostile, it was nothing more than stab-stab, over. Left lung, right lung, seemingly every time. They were lucky to even take a swing, and he never did get injured.
He's the one that single-handedly defeated a forgotten beast breathing necrotic dust. It wiped out two entire squads, Urist McStabby dodged in around it, stab-stab. And since it didn't die immediately, went methodically to work on its limbs. Stab, forearm flies off. Stab, there goes a foot.
I think he lost a tooth. He was there until the fort died FPS death.
My personal favorite: Urist McAsskicker.
First goblin siege, he gets conscripted, runs out of the fortress and passes by all the dwarves already on the way, and has a considerable lead by the time he met the first goblins to immediately...
Well, pass out in a pool of his own blood.
I'm surprised he survived to get to the hospital.
But survive he did, and he spent a long time in recovery. Over a year, I think. He was still there for the next siege, and saw the fresh wounded come carried in from the surface and most of them carried back out to the depths.
Once he did get out, he trained. And trained, and trained. If he wasn't eating or drinking, he was training.
Until the next siege came. He sprinted out to meet them, had a considerable lead when he met the first wave, and...
Utterly routed the siege among a shower of their own blood, minor digits and teeth. (Hah, got you on the suspense there!) On his own, before the rest of the squad even caught up to him.
So I remembered he was labelled a hammerdwarf, I'm going to give him the artifact silver hammer we've had laying around. He freaking earned that, and was going to wreck face wholesale.
Except I get cancellations. "Not enough hands." or something to that effect.
That first siege, when he passed out from blood loss? It was because the front sword-goblin had immediately lopped both his arms off.
So he had recovered and trained until he kicked ass at kicking asses. He had routed siege #3, singlezero-handedly, solely through kicking.