I thought I'd relate an event that ended a long campaign based in Mystara (an old campaign setting from the '80s for the uninitiated).
The PCs were all a bunch of rogue, desperadoes and just generally very unpleasant people. It consisted of a deeply racist orc, an insane barbarian (one too many hits to the head), an (annoying) elvish cleric, and my character who was a mercenary treasure-hunter.
The majority of the PCs had all been geased after falling foul of a very powerful cleric, and forced to end the life of an upstart snake creature that was striving to become a God in its own right. At first the group decided to resist the task imposed upon them, but when they started getting sick they had no choice but to try and complete it. Privately my character was thrilled at the news. He had not been geased, and being a hunter of rare artifacts it was right up his alley.
So the group entered the vast ziggarat that was this creature's domain. And it was vast. There were traps everywhere and nagas around each corner. Furthermore there was a band of catfolk who had infilitrated the same structure and were fighting a war of their own against the snake-men. Worse still when we finally saw the snake creature we were supposed to kill, any courage we had left us. It was huge and bloated and filled a 50'x50' room all on its own.
So the PCs decided to do the wise thing and run!
It was after we escaped that things got interesting. In our explorations we had come across a half-orc who had ignored us but was single-handedly slaughtering nagas. After we escaped the ziggurat the same orc approached us. He produced a dagger that he claimed was an artifact that could kill the snake-creature and he wanted to trade it. His reasoning was that he knew that we needed to kill the snake, and that he wasn't interested in doing it himself.
We looked at the half-orc. The half-orc looked at us back. We noted the medley of wonderful weapons the half-orc carried alongside the dagger. The half-orc yawned. We decided to overpower the half-orc and pillage his corpse. The half-orc changed into an bronze dragon.
Needless to say we all died a horrid and brutish death.