Continuing the series of 25 short horror-themed D&D adventures in September...
Adventure 3 - The Prison
Any forsaken wilderness; the traveling party discovers the lair of a hermit.
SETTING THE SCENE
The area is littered with carved religious icons and symbols built of local materials; wood, driftwood, soft pieces of stone. When he becomes aware of the travelers, the hermit comes to the mouth of the cave, yells barely coherent warnings to stay away, and throws a few rocks at the characters. His actions are interrupted by seizures and he heads back into the cave.
WHAT'S GOING ON?
Many years ago, the hermit was a devout priest attending an exorcism with an experienced bishop. The exorcism failed, the bishop died during the attempt, and the foul spirit entered the priest. The experience leading up to the exorcism strengthened his faith and he discovered he was able to keep the demon imprisoned in his flesh. He fled civilization for the wilds and chose a hermit's life; he would die in the wilds and his resting place would become the demon's prison. The cave is filled with etchings of magic circles and warding symbols that would keep the demon imprisoned after he passes; there are tethers he dons at night to keep his sleeping form from wandering away when he can't suppress the demon.
If the group approaches the cave, they might get close enough for the demon to attempt to possess a party member, especially while the priest is agitated and his self-control is lower. If successful, the demon is intelligent enough to lay low and leave the character "in control". The priest, long attuned to the demon's presence, will go berserk if it escapes him, and attack the characters with a gnarled staff, repeating over and over again that they can never leave.
If the party kills the priest, they can piece his back-story together from shreds of a diary and learn what they've done.
The demon will attempt to hop from character to character to sow confusion; it can be located with Detect Evil, and other bizarre effects may surround the character currently possessed - more buzzing flies than usual, curdles milk, that kind of thing. Splashed holy water and Bless spells will trigger reactions in the unwitting host; it can be trapped with Protection from Evil, removed with Exorcism, destroyed with Dispel Evil.
If the group returns to civilization, the demon will wait for an opportune time to seize control of the possessed character and escape into the world; by the time the others catch up, it's likely the possessed character has already caused quite a bit of damage, and the demon has fled elsewhere.
I wrote a previous post on using traditional "unclean spirits of the wilderness" as demons in D&D, providing game stats and interaction with certain clerical spells, you can see it here: Unclean Spirits of the Wilderness.
Locales: A forsaken wilderness, the hermit's cave
NPCs: The pious hermit
Monsters: The Demon