Slagswimmer
This symbiote comes from a world where it was necessary to travel through volcanic areas and endure immense heat, so the symbiote (changed some, of course), offers abilities reflecting that.
Host Type: Most mortal creatures.
Host Environment: The shoulderblades, right between the arms; partially burrows inward until needed for it's purposes.
Reproduction: The symbiote is not used to meeting others of it's kind, thus it has been pushed along (by bio-wizardry) to produce clone bodies of itself if a mate cannot be found; see Side Effects.
Hit Points: A mega-damage creature with 1D4x100 M.D. and impervious to fire and heat.
Average Life Span: Ten years outside the host, lifetime with it.
Alignment: Effectively a low animal unprincipled.
Powers: The symbiote may do the following things:
Bonuses: +2 to P.E., +2 to P.S., always resistant to heat and fire (half damage). The character gets some food value from ambient heat, constituting 10% of the charater's diet
Side Effects: If the symbiote becomes convinced it cannot find a mate, it takes 10% of the host's food (effectively neutralizing the bonus) and stores it to produce a clone.
Cold attacks do 10% more damage to the owner.
Size: About the size of a softball.
Means of Elimination: The symbiote can be convinced to leave using telepathy or empathy. One can also bait it with a member of it's own race, but this is less appealing. Surgery can also be done and will do little damage to the symbiote.
Market Cost: 10 million credits; somewhat specific powers, but a good selection nonetheless.
Note: If the characters makes a habit of swimming in lava, it develops his muscles and is a very good body-building exercise.