In Dungeon Magazine issue #85 is an adventure titled Lord of
the Scarlet Tide. Written for 3rd edition it is simple enough to convert for
5e. While the adventure as written is somewhat bland, the core elements can
slide into a Ptolus campaign with little adjustment.
The premise revolves around a trapped powerful aberration being partially freed. I'm changing things so that someone took a magical tablet (one of five) that holds the necessary information for keeping it imprisoned. The creature causes a fungal disease to spread from its prison far below the city. Getting the tablet back where it belongs and performing the ritual to recapture the creature or defeating the monster is the goal.
The ideas and some encounters lend themselves easily to Ptolus. The big bad could easily be Galchutt. There’s also a non-typical mind flayer using what can pass perfectly as chaositech. Infected townsfolk, a behir, kuo toa (who originally imprisoned the thing), and ghosts are encounters to be had.
I originally intended to use this in my first Ptolus campaign for one of my two groups. Never got around to it before the campaign came to a halt.
I planned to have Castle Shard send the characters to a high end auction being secretly held. They would be told as cover to bid on whatever they chose (limited budget of 2,000 gold) while remembering everything being auctioned and report back. That is where they would learn about the tablet and its connection to the disease, or similar info that helps put the clues together.
