Nice as for the quest idea. I was thinking about a ghost that had ran an entire village out. So your characters enter this place find clues as to why people deserted. Eventually the ghost starts posessing objects around you. You eventually find out this ghost is trapped in the inbetween. And the quest being optional is that you can capture it within a soul crystal (or whatever object that you would deem worthy) Eventually the quest gives a backstory of a woman who had murdered her husband and kids whilst asleep. The ghost is actually of the husband. A man who cannot move on from such betrayal and loss. And the only way to give him any peace would be to take his soul and capture it within the crystal to release into the netherworld but the twist could be you come across an automation. Think steam punk automations and you find that with the soul crystal you could effectively have the ghost possess this automation and control it. Being an extra character.
I dunno just some ideas from the spreadsheet thing there
