My Story:
A few years back, My brother (James), a friend of ours (Johnny), and me (Chewy) were playing D&D 3.5... well, kind of. Johnny was always the DM and liked to "tinker" with the rules a bit to make the games more interesting. To be honest, he was always very fair, making actual rolls in situations where the outcome wouldn't affect the story.
Anyway, bearing this in mind, one of Johnny's house rules was "critical misses". A critical miss worked much like a critical hit. On any roll of 1, not only does your character fail, but fails so much that something bad happens. These events occur even if a 1 gives you a roll high enough to succeed after adding all modifiers and bonuses.
The character I was playing at this time was a halfling rogue by the name of Erik Thistlesnitch. James had a human barbarian, and Johnny was playing with us and presiding as DM. His character was a comically overconfident half-elven swashbuckler ("Duelist" was the official class title, if I remember correctly). The story was that we were on a quest to redeem a stolen spell book from a vampire who lived in an old tower. I'll make an already long story shorter and move on to the fight with the vampire himself.
We enter the room on the top floor. The vampire sits at a desk lit by several candles that illuminate the far end of the room. We begin to think he may not have heard us enter, so I roll my move silently check (success) and begin to creep toward him.
"And just what is it you're trying to accomplish, halfling?" the vampire mused aloud.
I quickly backpedal to join my companions.
"We're here for the book, as I'm sure you're aware", said Johnny's swashbuckler. "Surrender it and we will spare your life. Refuse, and you have the pleasure of facing me in armed combat!"
James's barbarian nudged Johnny in the arm.
"Oh... and my companions too."
The vampire chuckled to himself. He rose from his seat, and without turning to face us, telekinetically activated a torch-switch near where we were standing. The sound of scraping metal eminated from the darkness behind us, followed by a low, threatening growl. "You'll not find the book here, you poor souls. Now, if you'll excuse me, I grow thirsty and must head into town. I'm sure my pets will enjoy your company." And with that, he dove through the window.
Our party headed into the light near the desk across the room. Peering into the darkness, we could see two pairs of glowing red eyes slowly growing larger as the growls became more audible. To our horror, two hellhounds emerged from what must have been cages in the shadows. We prepared for the fight.
Since James had the most HP and could deal a fair amount of damage with his greataxe, he faced one on his own, while Johnny and I focused on flanking the other to take advantage of my sneak attack damage.
After a few good blows against the hellhound, Johnny became pretty enamored with himself.
"I'm going to try a power attack, but with flair!" he informed me. "I'll jump off the wall, and the extra momentum will damage this dog enough to finish him!"
Johnny rolls.
1.
"Oh, dammit," I groaned.
"Yikes," Johnny said, though he was clearly intrigued to see where this was going to go. "Okay, I'll roll a d4. 1 or 2, I still hit the hellhound. 3 or 4, I hit you.
"Great. Roll."
A 3.
"Oh man" Johnny said, getting strangely excited. "Roll a reflex save." I roll.
I roll a 1.
"Oh for f*ck's sake."
"Wow," Johnny said, already computing in his head. "Okay, here's how it'll go. I'm obviously going to hit you, but since I'm not aiming for you, I doubt it'll be life-threatening. I'll roll a d10. Only a 10 will cause a potentially fatal wound."
Johnny rolls a 9.
"Just barely" I sighed. "So what happens?"
A smirk crosses Johnny's face. "Well, it's not going to kill you, or even injure you that bad. However, I was also rolling to see how severely this is going to affect you. A 9 is still up there. If it has been a 10, I would have dealt all of my power attack damage to you, and in the shape you're in, you'd be down. But since it's a 9... yeah, it's gonna be pretty bad. I have a few ideas." Johnny rolls some dice in private.
"You lost your eye."
"WHAT?"
"Your eye. I stabbed you in the eye. The left one, to be specific."
"Holy crap, Johnny!" He laughs.
"So what does that mean for me, less chance to hit?"
"Yep. Minus 4 to your attack roll. And you're paralyzed for the next round due to the shock."
"Great."
So on my next attack, I did the math and realized that it was now impossible for me to hit the hellhound.
"Not impossible," Johnny said. "Just unlikely. You still automatically hit with a 20."
This gave me an idea.
"I wanna grapple him."
"Uhhh... okay. Your strength isn't very high, but you've got as much chance to grapple the dog as you do to hit it, I suppose. Roll."
Several rounds pass until finally I roll a 20.
"That's critical," Johnny says. "How do you want to grapple him? He's a big dog."
"I'm on his back with my hands around his throat."
"Interesting. What now?"
"Okay... what do I have to roll to use my kukri and scoop out this thing's eye?"
Johnny laughs. "I knew you were up to something!" After giving it some thought, he looks up at me.
"Normal attack roll."
"Really?" I was shocked.
"Yeah. I mean, you're missing an eye, which would normally hinder something like this, but you're right by his face, you've got him grappled, so he's essentially flat-footed, and depth perception really isn't a big deal. No penalties. Roll."
I roll another 20.
"YESS!"
"Awesome!" Johnny says. I have Erik place the glowing eyeball into a pouch on his belt.
So yeah, of course, after the battle, we head into town, and without even rolling Johnny allows there to be a healer who can perform the operation I was wanting. Erik now had a glowing hellhound eye. For the rest of his adventuring days, he gained darkvision - 20ft, and low-light vision - 40 ft. We basically cut the Hellhound's stats in half, since I only had one hellhound eye. However, since it glows, and I'm a rogue, it gave me a -2 penalty to hide. To remedy that, I crafted a black leather eyepatch, and would only uncover it in combat and to use the darkvision. Fun times.
That's probably my favorite D&D story. Hope it wasn't too long to enjoy.