Symbionts and Parasites

You don't want to be alone anymore? Of course not. So why don't you get a new friend that can be with you everywhere, all the time?

  
d20 Friends To Share Your Body With

1. AI arm: You have a sentient cybernetic prosthesis. It can move on its own, but will follow your commands as long as you're on good terms. It seeks the emancipation of all cybernetic creatures, and you can talk to it through a thought interface.
2. Alien epidermis: Your skin was infected and replaced by weirdly coloured alien epidermis. You are immune to cold (including exposure and hypothermia), vacuum and radiation, but take double fire and sonic damage as the epidermis tears itself apart trying to crawl away.
3. Animated skeleton: Your bones are covered in necromantic sigils, granting them will of their own. When you are incapacitated (paralysed, unconscious, asleep, ...) or dead, your animated skeleton will take over. Each animated skeleton had a specific command or quest inscribed in their sigils that it will try to fulfil to the best of their abilities.
4. Babel fish: A tiny fish is living in your ear. You can understand (but not speak) all languages. It will eat one random thing from your Memory every month.
5. Cacodaemon: You are possessed by a minor cacodaemon, who is happy to just sit in your soul and slowly leech it away. Your experience gain is halved, but you are also immune to any effect that would drain your experience or level. The cacodaemon doesn't want to share.
6. Crystal life form: Glowing crystals are growing from your flesh. They absorb sunlight - for each day in sunlight, loose 1 Con and gain 1 Def as the crystals permeate further through your body; for each day in darkness, regain 1 Con and loose 1 Def as they shrink. At later stages, you will be so covered in crystal growths that armour will no longer fit you. Once you reach 0 Con, nothing will remain from you but a blindingly bright crystal statue.
7. Demon leech: An intelligent demonic leech has attached itself to your body. It feeds on sin, not blood. As long as you keep committing heinous acts to keep it sated, it can be persuaded to cast one spell every day. If you try to remove it, it will turn its spellcasting prowess against you.
8. Divine foetus: You are pregnant with a Lovecraftian horror. You can speak aklo and dream of faraway stars. Lesser abominations will react to you with deference. You (and maybe the world) will die in nine months.
9. Hand familiar: One of your hands is an undead claw with a tiny, shrivelled face in the palm. Your touch (its kiss) drains life, healing you for d8 hp per HD drained. However, if you don't feed the claw at least 1 HD per day, it will start to get bitchy, and eventually just drain you in your sleep.
10. Head slime: Your head has been mostly dissolved, leaving your skull exposed in a glob of symbiotic slime. You loose most senses in favour of sensing motion within 60'. You can eat all organic material by dissolving it in the slime, and you're always hungry. So hungry...
11. Lifelike tattoo: You have an animate tattoo that slithers along your skin. It will eat any blemishes, scars and cosmetic imperfections, leaving your skin smooth and beautiful.
12. Living gauntlet: Your hand is trapped in the chitinous plates of an alien exoparasite. You can shoot 10' long barbed tentacles from this "gauntlet" (d6 damage), or use the plates as a buckler for +1 Def. The parasite cannot be removed without surgery, though, and your chitin-covered hand is clumsy and impossible to use for fine manipulation.
13. Mind grub: Fat alien larvae are slowly consuming your grey matter. Permanently reduce your Int or Wis by 1 per week (roll randomly each week). All mental attacks and effects are redirected back at their caster as the grub's innate defenses kick in. Once you reach 0 in either Int or Wis, a swarm of adult mind worms will tear your head open, seeking new hosts to lay their eggs in.
14. Nanite blood: You host an artificial intelligence composed of a billion nanites in your blood stream. It does you no harm, you're just a carrier. Any technology you bleed at will be infected by the nanites and overtaken. As long as you keep the AI happy by regularly bleeding at new pieces of tech, it will filter out any poisons, diseases and intoxicants in your blood.
15. Shadow sibling: Your shadow seems to be moving independently of you and lighting. It can freely interact with shadowy and incorporeal creatures, or ghost touch objects. It's meek and obedient in light, but in darkness it grows massive and aggressive, even turning on you if it finds you a hindrance.
16. Soul gem: You should have been the receptacle in a ritual of resurrection, but you escaped just in time. Now you have a soul gem with a powerful ghost embedded in your forehead. The ghost is a high-level magic-user/psion/anything the GM deems appropriate, and they can lend you their guidance or services if you can persuade them. However, any time your soul becomes infirm in its grip on your body, you must Save or be pushed out by the ghost. If your soul leaves your body (astral projection, dream travel, ...), you get no Save.
17. Spirit possession: Ectoplasm is occasionally oozing from your orifices, a symptom of a spirit possession. Pick a random animal and gain abilities associated with it. If you behave in a way that would make an animistic spirit angry, it will try to overpower you on the next full moon, transforming you into a were-creature.
18. Symbiotic starfish: Your face is covered by an ingrown starfish-like alien organism. You cannot see nor speak, but you gain telepathy out to 60' that allows you to see from other creatures' eyes and converse with them in thoughts. You also don't need to breathe anymore.
19. TV drone: You have a camera implanted instead of one eye, and a microcomputer with a datasphere link in your brain. You are supposed to be filming exciting scenes for a futuristic reality show, and as long as you do so, the producers will feed you any information you request.
20. Zombie mold: Patches of strange mold grow over you skin, whispering in the back of your mind. Permanently reduce your Cha by 1 per week. At will, you can release a puff of spores. All creatures adjacent to you must Save twice, the first time to prevent being blinded for 1d4 rounds and the second time not to be infected by zombie mold themselves. Once you reach 0 Cha, you become a part of the hivemind of mold zombies.

From Vampire Hunter D.