Working on a new adventure for the blog (A 5-minute adventure ... anyone remember those?) for White Box S&W. below is one of the hazards the players will contend with.
The cavern was like some dark god’s garden. Statues of animals, people, fae in all manner of poses and situations littered the place. The floor was black and smooth to the touch. It was beautiful in its way, deadly too.
Obsidian Slime is less a monster as much as a hazard of the deep underground. Obsidian Slimes grow on the ceilings of mane caves and appear to be as hard as the black glass they resemble. However, this is but a default defense for the slime to protect it from any creature that may try to harm it. When not hard the Slime is tar-like and typically drips from the ceiling of a cave. Any living thing that comes into contact with the Obsidian Slime is doomed to become Obsidian Slime (Save negates). It is immune to fire and ice and the transformation can only be postponed by a cure disease spell. Once the Slime enters the body it will always be there.