This wasn't something brutal that I did but it was something i was on the receiving end of...
I was wandering through a goblin capitol with two mates trying to find and liberate their children. We're stopping at every villager we found to try and get answers and limbs off of them but are having no luck... with the answers bit... lots of luck with the limbs.
We slayed many a goblin villager and guard alike. As an odd side-note... the trolls just sorta watched... they didn't seem to mind that we were slaughtering their longtime neighbors wholesale... oh well. Eventually we stumble into the throne room and we spot the goblin lord who immediately flees at the sight of 3 adventurers fully armed and coated in fresh goblin blood. Thinking that maybe the lord will know where the children are being stowed, we gave chase. We finally caught up to the Lord and quickly dispatched him after we learned he had no information of use to us, but this was a mistake...
His master was waiting in the very room that the Lord had led us too.... a feathered monkey demon that breathed fire and undulated with a power unknown. I yelled at the demon that we don't wish to fight but he looked at me and slyly said "ah good, it's spearblight, the slayer of (The Local Goblin Lord we just killed)." I began to try and turn back, I had never encountered a demon before, but there's no part of "undulating with power" that sounds like it'd be a pushover.
Before I could back out of the fight, my companions had already spotted the beast. Being too confident from their recent civilian murder-spree they turned from the slain goblin lord and moved for the demon. In a moment of true foolishness, I decided that maybe it was possible with the 3 of us. I was wrong.
As I go in to make the first strike, I go to swing my halberd for the monsters throat. Before the blow could connect, the demon simply caught my weapon mid-swing with it's bare hand and brought back it's other. It's other hand lashed out with it's menacing claws at lightning speed. I didn't stand a chance, his claws cut through my iron greaves like paper and one of my legs went flying across the room. Before I even had time to react, the demon pulled back it's hand and reformed it into a fist. He then punched me int he chest with the force of a battering ram. Almost all of my internal organs were pulped instantly and I went flying after my severed leg.
I lay there immobilized, alive just long enough to see the demon dispatch my companions. The first of the unfortunate fools never even reached the demon, being casually dispatched by the demons fire and his quest ended in a smoldering pile of ash. The other got a bit farther, only to have the demon turn on him with my very own halberd. The demon monkey took one swing and my companion was separated at the beltline. In my adventurers very last seconds of life, he saw only the back of the monkey demon as it walked away, coated in me and my companions blood and holding my precious halberd.
This whole event happened all within a few moments. My leg hadn't even landed yet before I was sent into the air. And my crispified companion got crispied before I even landed...
Long story short... do. not. underestimate. demons.