Well Gorgon Milk's blog for a few resource I can use in this case Underworld Lore Issue #2 which concentrates on dungeon born diseases, gods, and other sundry horrors.
Grab that right over HERE
In the article Preternatural Pestilences has thirty or so random bits and pieces of nastiness that can be inserted into any adventure as set or dungeon dressing but in my case its going to be the center of tonight's encounter. Now on page thirty eight is a rather nasty version of an infectious fungus which is actually a low level monster.
Crave Fungus is another version of infectious fungal dungeon monster , which is a fungal horror that shoots out spores into those who disturb this menace and the stuff takes them over from the inside out. This is not a new idea I can assure you and goes all the way back to William Hope Hodgeson's Voice in the Night and “Fungus Isle” by Phillip Fisher from the October 27, 1923, issue of Argosy All-Story Weekly, later it was reprinted in “Fungus Isle” was reprinted in Famous Fantastic Mysteries in their October, 1940, issue. There's an entire history and very good cross comparison of these two story right over Here. Now given the passion for fungal sporemen and shroom people in D&D style games I think that these lifeforms might be a part of or product of the shroom people from the Monster Manual two. I'm leaning towards a Boot Hill 2nd/AD&D 1st edition crossover.
A town known as Riven Gulch has sprung up almost overnight in an alternative Weird West setting. There is a mega dungeon that is been producing some rather valuable relics and other worldly treasures and folks are flocking from all over to get in on the action. The Wells National Bank has set up shop in town and is handling many of the transactions of this place. Folks are striking it rich and making out very well. So the bank is a nice rich tempting target.
What no one in town realizes is that others eyes have been watching the various comings and goings of the explorers, adventurers, and professionals into their underground world. And the cycle of birth, rebirth, and degeneration. Now the PC's have stumbled upon a 'deserted' town and interesting hi jinks waiting to happen.