Good question! I made my own one-shot for Halloween. It hasn't been play-tested, but if anyone out there interested in helping me improve it, or if you want to try it out, here's a link:
Apologies in advance for typos and editing errors, and thanks in advance to anyone who has a look.
Here's the pitch/summary:
In an ancient, long-dead empire, a cult called The Red and The Black figured out how to use the blood of an abominable creature, the Death Spider, to perform powerful rites, including resurrection. They built their temple in the subterranean caverns where the Death Spider lived. Fast forward to the present, where our adventure begins. The player characters start in a room in the ruins of that long-dead underground temple. They are unable to remember how they got there. You, the GM, know that days before, they came there looking for treasure, a missing comrade, etc. – whatever is convenient for your game. The key thing they do not know is that they died searching the temple, and now they are ghosts.
As the characters move through the underground temple, they will discover many things. They will find their own dead bodies. They will figure out that they are ghosts. They will learn how to conduct the ancient resurrection ceremony, reunite their spirits and bodies, and bring themselves back to mortal life – a task that first requires them to extract the blood of the horrid abomination called the Death Spider. In the process of accomplishing all these tasks, they will move through creepy underground caverns, be stalked by Death Rakers and other monstrosities, and meet with all sorts of horrifying sights.