Symbiont

A parasite is any creature that invades a host and thrives at its expense. Once it has made itself at home within or adjoining the body, it could potentially cause one or more subsequent effects. Possibilities include injecting venom, spreading disease, draining some vital resource (e.g. oxygen, blood, food, water, MP), laying eggs, or even taking complete bodily control. Some parasites actually cause beneficial effects in place of or in addition to detrimental ones, such as heightened strength, speed, durability, influence, or immunity.

When a parasite intrudes upon a creature, it must make a Vitality check. Those who pass the check render their own bodies inhospitable and eject or destroy the invading organism. Creatures who fail the check become easy prey and face the side effects, whether beneficial, detrimental, or some combination of the two. Most parasites remain until resources dry up. Some live for mere hours but others endure for a lifetime.