Creeping mold is a common monster in many role-playing games and fantasy fiction. This particular mold goes under a whole stable of different names in computer rpgs, but they are all similar in what they can do.
This mold is unique in the fact that is has the abilty to move slowly over any surface, at about the speed of an old person walking. Creeping mold will usually be brown in color, and has a very distinctive smell, kind of like mustard. They can grow to very large sizes if kept well fed, but like many mold/fungus mosters, they will eventually break up into multiple creatures if they grow large enough.
The creeping mold spends most of its life slowly moving around in search of moisture (sucking up small puddles, and the like). But they will attack any creature who gets within a few feet of it, either by dropping from the ceiling, or by quickly rushing onto them from the floor (they can move faster when attacking). The mold will then proceed to suck all the moisture out of its prey, leaving behind a withered corpse (from which a new mold will be born in less than a day).
The creeping mold is especially deadly because it is fully immune to most form of attack. Salt, acid, and electricity are the only way to destroy one of these beasties (although fire will often drive them off, it does no real damage to them).