I can't recall the bloodiest death i've had, but the bloodiest battle i've had was with an Ettin (damned things)
I had some companions with me, and I was playing a heavy armored pick dwarf, the ettin was maybe my twelfth quest on a major character. I can't recall it's name, but it had a 3 page long kill list before i fought it. Almost all off my companions were killed quickly, usually by the ettin grabbing people, gouging out eyes, throwing people so hard they burst on contact, breaking limbs, and at one point punching out an arm from a poor son'uva and beating the next person to a pulp with it. The room looked like a torture chamber, however thankfully I was doing damage with my pick, tearing limbs, i broke his limbs, bruised his organs, i think i ripped a foot at one point, but my pick got stuck in the ettin's upper chest, and that was where the battle took a wrong turn.
Ettin broke my grip with the pick, and while the last companion was fighting, somehow, and i have no idea how, in a span of 1 action for my character, he took the pick out, tore off a limb from me with my own weapon, and while i was spewing blood the beast grabbed me, gouged out my eyes, and threw me against a wall. My legs were smashed to pieces and my only arm was torn apart, I was still alive though. Watching the ettin stick the only companion still alive in the head with my own pick, it was so horrible, and he rushed over towards my shattered body, and crushed my head.
The gore was so massive, there were dozens of limbs strewn about, and mangled bodies everywhere, all the blood... Damn ettins