As you might notice from the list of characters below, none of the characters had actual names. As is the old-school rpg trope, the characters were referred to only as their "class." I guess Gary was a bit of a grognard, eh?
Also old-school was the nature of the adventure. I used a hacked-up version of "The Death Ziggurat," which is mostly a randomly generated hexcrawl with a few detailed locations.
Characters
Mortuary Knight
Funereal Priest of Kalag-Mohr
Ossuary Cryptarch
Order of the Scarab Assassin
Ranger of the Thornwoad
Dustspeaker of the Empty Hell
Events
Beyond the Black Goat's woods, the party found a deep depression filled with ruins--it looked as though a giant fist had pummeled the earth. They located the camp of a fearful group of cultists clad in furs, outlandish headdresses, and dangling bits of bone. The cult's leader brought them to the cavemouth that could lead into the depression. This was a literal "cavemouth": its rocky fanged jaws were clamped shut, but they opened when the Ranger of the Thornwoad bled upon it.
They explored as they moved north from the cavemouth. Strange phenomena occurred as they traveled. At one point, the daylit sky turned to black night and a hole that was darker than darkness could be seen expanding in the sky. (This was a callback to "Black Hole Sun" playing in the Velvet when the agents went to stop the handoff of Gary's art.) At another point, snow began to fall from the black hole in the night sky.
The group encountered a pack of priests in black robes with wide-brimmed black hats and veils. The priests attempted to warn them off of venturing further through the ruins, then warned them of Arkuhn, the Child of the Cosmos, Daughter of the Black Goat. The group ran for it as Arkhun approached--they didn't even stop to get a look at her.
After fleeing from Arkuhn, the party discovered a spiraling chapel. From the top of the chapel's spire, they saw a frozen lake and smoke rising from an encampment of some kind, but they did not see the ziggurat they sought.
They decided to head for the encampment to see if they could gleam any information as to the ziggurat's whereabouts, but they never made it there. On the way, they encountered another pack of Arkuhn's rot-priests and two dark young of Shub-Niggurath. The priests really latched onto the Ossuary Cryptarch, chomping away at his flesh while the others fought off them off. Somehow, he survived.
They searched the priests' bodies after the melee and discovered that they all wore medallions that held hidden keys. Now that they had these, they decided against visiting the encampment. Instead, they headed for the frozen lake. The lake was surrounded by moaning undead whose feet were stuck in the frigid mire. They ultimately decided that they didn't want to mess with that.
Heading north again brought them to the spiral chapel again. However, those who now had medallions could see a swirling tornado of fog partially obscuring a black ziggurat that they hadn't been able to see before. Investigating the mural of a priest surveying the cosmos also netted them a crown that was bladed on the inside. The Ossuary Cryptarch removed the blades from the crown, but it didn't do anything when he put it on.
Those who had medallions had to lead those who did not, but they eventually pushed their way through the fog tornado and up the steps of the black stone ziggurat. At the top of the ziggurat, they used three of the keys to unlock a "scab" that led straight down into a pulsating "throat" of flesh. They shimmied down the wet flesh tunnel and found themselves in a meaty cavern where a large heart was beating.
They also found Arkuhn, a floating child with too many eyes, goat horns, and a toothy maw running vertically down her body.
While the rest of the group engaged Arkuhn in combat, the Order of the Scarab Assassin stabbed the heart, killing it. (This was a wise thing to do; if the heart wasn't destroyed, Arkuhn would have kept resurrecting.) The Mortuary Knight hit Arkuhn hard enough to send her spinning out of control. The Funereal Priest's devotion gave everyone the zeal to hit harder, and the Ranger of the Thornwoad peppered Arkuhn with arrows--until her bow was damaged. The Dustspeaker of the Empty Hell tried to demoralize her to get her to flee, but Arkuhn held strong in the face of adversity. The Ossuary Cryptarch stabbed Arkhun with a blade from the crown, but this healed her--undoing a lot of their hard work to slay her. She relentlessly blasted them with bolts of cosmic evil from her eyes. Ultimately, the Order of the Scarab Assassin leapt through the air and stabbed the eldritch child to death.
The grim party who had fought their way beyond the Black Goat's woods had triumphed. Their world was safe from Shub-Niggurath's influence.
But what of the echoes that would reverberate across other worlds? Well, we'll tackle that in the last of these Halloween one-shots.