Cave of Six Seals

Do you dare delve into the depths of an ancient demon's prison?

Designed to be a fun 5E challenge-dungeon. Delve into a cave where an ancient evil was once sealed away... but be wary, as over the ages, the seals upon the Demon have begun to weaken...

This is the one-shot featured in my larger adventure, Tower of the Chronomancer, but more polished and slightly expanded to allow it to stand on its own. (Originally it was the Tower's "6th floor.")

I'm making this Pay What You Want, hoping people will enjoy this content -- and maybe seek the larger adventures I've already written.

The Cave.

Mostly hidden behind a nondescript hill in a crowded wood, forgotten by almost everyone not of the nearest town, and even they have forgotten why the cave was originally created. What it contains -- what it seals in. Marked only by a broken, rotten sign, now it's viewed as a prank spot. Sometimes it's a hideout for unsuspecting bandits. Generally, it's a place no one goes on purpose due to the lingering "wrongness" that any who enter seem to feel.
Any that pass through the perfectly-rectangular entrance will find that it's much more than meets the eye. Especially if they are able to find their way down to the Trials!

The Story.
Long ago, a shapeshifting demon called "Umbraeus, the Defiler" sought dominion over the world. It clawed its way out of the Hells and took control of the region through a mixture of trickery (empowering people it could use) and destruction (raining fire, destroying crops and rivals, etc.). Umbraeus reigned for many years... until it was betrayed by a rival, which allowed a group of adventurers and mages to defeat and trap it in a magical green gemstone.
The gem was then buried deep underground, protected by a set of Trials that allowed only those pure of heart and capable of handling its influence to visit it.
But a long time has passed. The seals that held Umbraeus at bay have begun to weaken. And the demon has found a way to crack the gemstone. Its malevolent influence has begun to seep out into the world above. If nothing is done, it may manage to fully escape!

Includes:

A 5e one-shot adventure for 5th-6th level adventurers (4-6 hours long)
Combat, roleplaying, puzzles, discovery, randomness, and loot!
A chalenging demon encounter with variable difficulty levels
6 original enemy statblocks, including an evil shadow-boss
2 original magic items.

Keywords You Can Expect:

High fantasy, cave dungeon, combat, evil demon, shadow dragon, puzzles, discovery, randomness, gelatinous cubes, constructs, moral quandries, and lots of loot.