What was your most impactful RPG session?
Hands down, it was the session in which my friend Trina's minotaur nearly murdered a paladin in cold blood.
We had been playing D&D 4e for some time and the characters were working their way through Gardmore Abbey. They had met a paladin of Bahamut in the town nearby and had agreed to help him find something in the abbey. I don't recall exactly what was happening with that, the important part is that he was traveling with them for quite a while. During their expeditions into the ruins of the abbey the group had come across a demonic shrine that was dedicated to an ancient creature that may have had a hand in creating the minotaurs thousands of years ago. Trina's minotaur was cursed by the shrine and started having conversations with the demonic creature when she would sleep. The creature urged her to cast off her domesticated role, embrace her true heritage, and return the minotaur race to their former glory. As things went on, he started dropping hints that the paladins of Bahamut may have had a hand in the downfall of the minotaurs. This manipulation went on for several sessions, and she became more and more unsure of their paladin companion.
All of this came to a head at one point when Trina's minotaur confronted the paladin with his order's history with the minotaurs. The paladin didn't deny that his order had something to do with the subjugation of her ancestors which infuriated her even further. She drew her weapon and challenged the paladin to a duel to the death. Realizing she'd been misguided by some demonic presence the paladin didn't draw his blade, but instead cast off his breastplate and told her to kill him if she was confident in this course of action.
It was an amazing moment. Trina's minotaur's resolve crumbled and she realized she'd been led astray. She didn't kill the paladin and had a lot to think over.