This thread reminds me of one I saw a while back. Mainly just brainstorming material for making the players sad. Well, the DM in the campaign I'm in apparently also saw that thread, because something similar to one of the ideas that got thrown around ended up as a quick, one shot encounter that we happened across while traveling between towns.
We were approaching a frontier town and ran across a pair of statues by the road. The quality and expressions made it obvious that they were people who had been petrified. A group of similarly equipped people a short distance away confirmed that their party had been attacked by a medusa and they had lost two of their number before they fought it off. We tracked the medusa to its lair, an old ruined temple.
We found what had obviously been its home, but no medusa. We also didn't find the collection of people-turned-statues that we thought we would, which meshed with what the residents of the nearby town later told us. They had never even heard of there being a medusa in those ruins, and had certainly never encountered one. Only the group that we had run into on the road had.
What we did find was a large collection of letters. Apparently the medusa had started writing letters to a man in the nearby town. At first pretending to be a girl who had spurned him, then after a while as they grew closer she admitted who (and even later what) she really was. They eventually agreed to meet.
We also found a note, addressed to whoever might find and read it, explaining what had happened. The man had arrived at the ruins at the same time another group was exploring the ruins, investigating rumours of a monster hiding out there. And while the group nosing around in the ruins didn't find her, he did. He startled her, saw her, and turned to stone. The note went on to say that she was leaving the ruins to find some way to cure him. There was one more note after that one. At that point the DM handed each of us a piece of paper, which read:
"I'm such a fool. Of course a lone woman traveling the High Road would look like an appetising target. I got two of them, but I took a bad hit. Even with the supplies in my pack I don't know if I would make it, and I lost it in the fight. Without it I won't last the night.
"At least I'm not alone anymore.
"I'm such a fool."
After a short while longer exploring the ruins, we found a solitary statue of a man, looking startled. The statue had been decorated with wreaths and flowers, and curled up at the statue's feet was a dead medusa.
We went back and found the group from the road. They asked us if we had found the monster. We replied that we had, and proceeded to kill the lot of them.
Transcription includes some very minor spelling and punctuation corrections, and changes it to conform to regionalised spelling that stops making my spellchecker yell at me. Is otherwise word-for-word accurate.
Reminds me of Witcher key narrative theme "who is the real monster here?"
Both books and the games are filled with plots containing similar kind of twist outting spotlight on vileness of character and not the nature.