Cordyceps Spore

Death Burst. The cordyceps spore explodes when it drops to 0 hit points. Each creature within 20 feet of it must succeed on a DC 15 Constitution saving throw or take 10 (3d6) poison damage and become infected with the Cordyceps disease on a failed save. Creatures immune to the poisoned condition are immune to this disease. The disease is transmitted through contact with the skin, so holding your breath is not sufficient protection.

Disease effects:

Once infected, the victim's body becomes a breeding ground for the cordyceps fungus. The infected creature will feel nauseous and dizzy and may begin coughing as well. He must begin making a Constitution save (DC 12) every 1d6 hours. 

After the first time he fails one of these saves, he becomes Poisoned. While Poisoned by this disease, the victim will desire to reach higher ground or more crowded areas, whichever is easier to reach. He will be unable to sleep naturally and cannot benefit from rests. 

After the second failed save, the victim enters the final stage of the disease and begins to show visible signs of the fungus such as mold on the skin, mushrooms growing from orifices, etc. He will be totally obsessed with crowded areas or higher ground and will not be interested in anything else. At this point the infestation has spread so thoroughly that only a Greater Restoration spell (or similar greater effect) can remove it. 

After a third failed save, the creature dies and becomes a Fungal Zombie one minute later. This can be delayed by a Gentle Repose spell.

If the creature is killed before becoming a fungal zombie, it still becomes a fungal zombie 30 minutes later (or 1 minute later, if it was already in the final stage of the disease)

Burst. The spore moves into another creature's space and attempts to collide with it. The creature must make a saving throw (DC 13) to avoid it. If the save fails, the spore explodes on contact and triggers its death burst ability.