Symbiont

A symbiote is a creature that "visits" another creature's body (and if it likes the place, it just might move in). Some are commensalistic, causing beneficial effects, offering boosted strength, speed, sanity, durability, influence, or immunity. Others are parasitic, invading their host and thriving at its expense. A parasite could inject venom, impose illness, drain some vital resource (e.g. oxygen, blood, food, water, MP), lay eggs, or even take complete bodily control. There are also symbiotes which both assist and harm their hosts.

Most symbiotes by far are tiny. Many are invisible to the naked eye. Others are large enough to fight in combat. Regardless of its physical dimensions, when a symbiote bonds with or intrudes upon a potential host, the creature must make a Vitality check. Those who pass the check render their own bodies inhospitable and repulse, 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 symbiotes remain until resources dry up. Some live for mere hours, but others endure for a lifetime. Some badass symbiotes can even outlive their host and seek a fresh one. A creature can serve as host to multiple symbiotes at a time — whether the tenants decide to share is a different story.