This is adventure 16 of 25 that is roughly designed to take characters from level 1 to 25 that I will be sharing over the month of September. These posts are a part of Asshat Paladin's OSR Short Adventure Challenge, and utilize his Get Ready, Get Set, Go! format.
Crack of Dawn
A Get Ready, Get Set, Go! Classic D+D adventure set in the PC’s Castle
The Hellmouth remains cracked open, and it’s getting bigger.
The remaining small crack of the Hellmouth continues to expand. As it’s necessary to have the Dawnstone to open the portal, it’s necessary to use the Dawnstone to permanently close it. There are a variety of ways that the PC’s can discover this. A Commune, Contact Outer Planes, or Lore Spell may reveal the info. Sages are another source. The end result of their investigation is an hour long ritual that will result in sealing the Hellmouth permanently!
While the ritual will indeed seal the Hellmouth, the final portion of the ritual opens the Hellmouth for at least 10 rounds before it is finished. During this time the Lords of Hell will attempt to disrupt the ritual with Goat Horned Demonic Beings. If they succeed, the Hellmouth will remain open. If they fail, they will send a fiery missile through the portal just before it closes that will arc out beyond the castle walls, and well off into the wilderness.
Large Goat Horned Demonic Beings (AC 4, HD 12, Attack: 1 Claw (4d6)/ 1 Bite (1d10+1 random ability point)