Putting it together, we've got something like this:
Gray Mold (CR X)
If disturbed, a patch of this mold bursts forth with a cloud of diseased spores. All within 10 feet of the mold must make a Fortitude save (DC Y) or be exposed to the disease below.
A patch of gray mold has 5 hit points, spell resistance Z and vulnerability to light and cold effects. The mold goes dormant for 1d8 minutes if a cold attack penetrates its spell resistance. It also goes dormant while exposed to direct sunlight. It takes 1 point of damage per minute when within a light spell or indirect sunlight, and 1 point of damage per round when when within direct sunlight or continual flame.
Gray Mold Spores (Ex): disease - inhalation, Fort DC X, incubation period 1 minute; damage 1d6 Con.
Unlike normal diseases, gray mold spores continue until the victim reaches Constitution 0 (and dies) or is cured by a remove disease spell (or similar magical effect) or a DC X Heal check. A patch of gray mold will grow from the corpse of a creature killed by gray mold spores.