OSR: Fantasy Prosthetics

The Death and Dismemberment Table is harsh. Adventurers are likely to lose digits, eyes, and limb. In theory, though I don't have any options to support it currently, they could even start without them. Sometimes, taking an Early Retirement or Retiring to Safety is the only way out, but rich, ambitious, or desperate characters might seek ways to remain ready for adventure.

Late eighteenth century beggar, clearly a former soldier, with two wooden legs. A. Smit after Pieter Barbiers. (Rijksmusuem.)
Taken from this article.

Basic Tier

Available nearly everywhere. Made from locally sourced materials (wood, leather, bone, iron, etc.).

Artificial Leg / Peg Leg: reduces Movement by 2. If both legs are replaced, user requires crutches, and can only wield daggers or other small weapons and at a significant penalty.

Artificial Arm / Hook Hand: cannot use the hand. Sharp hands deal 1d4 damage on a hit. Slightly fancier versions can have alternate attachments (fork, knife, pen, etc.) or support a shield. If both arms/hands are replaced, user cannot wield weapons.

Eyepatch / Mask / Wooden Eyeball: covers the hole(s) in your head and some of your scars. No bonuses but it might stop people from staring.

Fancy Tier

Masterwork creations of clockwork, springs, wire, and wood, these expensive non-magical replacements are only available in large cities. They take at least a month to build and test.

Artificial Leg: Reduces Movement by 2. Can include a hollow compartment that can hold 1 dagger, 1 wand, or 1 vial of liquid. If both legs are replaced, user requires crutches, and can only wield daggers or other small weapons and at a significant penalty. Has a knee.

Artificial Arm / Mechanical Hand: can use the hand for some tasks, but cannot wield weapons. Deals 1 damage on a hit. Makes a distinct ratcheting sound. Extremely fancy versions can have a concealed dagger inside.
 
Glass Eye / Silver Nose / Painted Face Mask: covers most of the damage. May only be noticeable within 5', and even then only if people are paying attention.

Pamplona Bible 1197, Bibliothèque municipale, ms. 108, fol. 179r

Magical Replacements

The soul is approximately the same shape as the body. This explains why ghosts have mostly human forms and why absent limbs "tingle" or experience false pain. After a traumatic injury, it can take the soul a long time to adjust to the body's new proportions.

A magic prosthetic limb simply replaces the original, trapping a portion of the user's soul in the same  manner as an enchantment (or undead binding, though few artificers relish the comparison). For maximum integration, a magical prosthetic must be permanently fused with the user's bones and flesh.

1. Troll Limb
The cheapest and deadliest method. Find a troll of a suitable size, lop off a limb, and stick it on to your bleeding stump. Stitches are useful for the first few hours. If your immune system survives the shock, you'll have a fully operational and mostly obedient new limb. A troll arm is considerably stronger than a human arm (+1 Strength) and regenerates damage just like a full troll. If the user dies or suffers a serious illness, the troll arm colonizes the body, takes over, and creates a new (if somewhat undersized) troll.

2. Living Wood
A misnomer; the wood is usually dead and varnished. Carefully fitted silver joints, wood measured and carved exactly to match the user's other limb (if possible), and layers of delicate enchantments can replicate the form and function, if not the feel, of mortal flesh. Such items are legendary works, kept as ancestral relics or produced by master enchanters for royal patrons. Their owners would be wise to keep the limb covered near avaricious wizards.

Desperate fools sometimes attack dryads to use their limbs. It could work in theory. In practice, death and misery are the only results.

3. Ghost Limb
Enchantments bound to the stump stabilize the soul-projection of the user's arm. (Ghost legs, while possible, are significantly less useful.) The arm is ethereal and invisible, but it can lift intangible items, interact with illusions, hold ghosts, and sometimes meddle with poorly designed magical locks and enchantments. A sufficiently magical or self-willed person may not even need extra enhancement to wield a ghost limb.

4. Fire Limb
The sort of thing undergraduate elementalists invent to deal with coursework-related injuries. Fire limbs fuse a fire enchantment to the user's soul. The user can project a mostly functional limb made of flame. Unarmed attacks deal 1d6 fire damage, but the limb also deals 2 damage per round to the user. It's more of a fashion statement.

5. Skeleton Graft
Bone remembers. Skeletons are soul-shaped containers just waiting for a spare soul or suitably crafted spell to hop in. Necromancers can attach a dead limb (the user's, if available, is best) and use a few simple techniques to convince the user's soul to inhabit the remaining structure. Users often report unpleasant cold shivers and vivid nightmares. A skeleton arm is a great way to meet the local authorities and see an spontaneous community-based bonfire event.

6. Gem Eye
Fairly common among wizards. Find a suitably large gem, enchant it, bind it to the user's soul, hope for the best. Poor-quality enchantments provide a smeared oil-painting view of the material world. The finest let users see souls, magic, ley-lines, magnetic fields, or the location of the stars during daylight.

7. Illusions
Elf Wizards can beautify and de-age a target with magic. This can't replace lost limbs, but it might restore hideous facial wounds,  missing teeth, and other perils of adventuring.

João Bragato

8. Crossbow Limb
Is this a good idea? Probably not. But some people are going to try. The enchantments are just to ward off infection and stabilize the bow.

9. Snake Limb
One of those rituals wizards read about in books and shrug off as fiction. Find a suitably large snake (none from Around Here; maybe in Foreign Parts). Cut off its tail and bind it bone-to-bone. Mingle the snake's soul and the user's soul in a high-power marriage ceremony. The user gains a limb with astonishing flexibility and a potentially venomous bite. The snake gains free meals forever. Some personality changes are inevitable.

10. Powderkeg Leg
Invented at least three times on three separate occasions, a powderkeg leg contains a powerful magical or conventional motive force. The user might hop twenty feet on a smoking column of fire or sail gracefully across a canyon on a beam of raw magic. Lightning strikes, botched landings, and the wrath of people they crash into tend to shorten the lifespan of their users.

11. Enchanted Armour
Plate armour can sometimes be enchanted to combat the deficiencies of its occupant. Despite being blind, nearly deaf, dropsical, and eighty-nine years old, King Gundobart the Bad of Waxburg famously killed twenty knights in at the Battle of Bogwell, though it is documented that four knights were from his own retinue. The king's enchanted armour gave him great strength and ferocious battle-sense, if not the finesse that he might have desired.

12. Golem Limb
Baked clay and a carefully worded scroll. The user must speak commands: "step", "grasp", etc, but the limb often functions with all the strength and ability of a flesh one. A mis-spoken command or a damaged scroll can lead to disaster.

13. Mindspikes
Found in forgotten tombs or carved from the un-spines of mind-devouring parasites, these fabled implements allow one creature to experiences all the senses of another. Blinded and scarred wizards might drive one spike into their own skulls and a second into a trusted acolyte or loyal familiar. 

Dan Mason

14. Fingerworms
Fat pink worms with lamprey mouths. Stick them on your finger-stumps and they obey your commands and suck on your blood. They're not as strong as normal fingers and they tend to alarm people if discovered. In fact, why are these things even on this list? They're gross.

15. Force Projection
Rather than a full limb, a properly aligned spell creates a permanent force-plate where the foot or palm of the user would normally rest. It's only as effective as a peg leg or hook hand, but it's completely invisible. Swords and tripwires pass right through the space between plate and the stump.

16. Ear Trumpets
Screwed directly into the brain. In theory, they could be enchanted to merely replace lost hearing, but why stop there? Hear through walls, translate languages, detect secret whispers of conspiracy and murder. Wizards tend to go a little overboard. Prolonged used leads to madness.

17. Magic Blaster
More than one wizard, clutching the stump of their shorn-off arm and surveying the remains of their latest disastrous experiment, has wished for a cannon-hand. The process is very basic and only requires bone-level integration if the user wants to trigger the device at a thought. The wand-limb can fire anything a normal wand could; some have slots for several devices. Be prepared for the recoil.

18. Grappling Limb
Fires up to 20' of rope or chain with a magical claw on the end. Yanks the user around. This might seem convenient but the strain on a user's frame inflicts 1d6 damage with each use.

19. Omnieye
Paranoid wizards enchant orbiting eyes or spinning spheres that can look in all directions at once. Someone with 360' vision is difficult to surprise but rapid movement or tumbling results in crippling nausea. The presence of a medusa is also unwelcome.

20. Mutation
Just pump a whole bunch of raw magic into the afflicted area and see if something useful bubbles up. What's the worst that could happen?

Nikola Matkovic

Replacement Parts as Treasure

Put some of these in your dungeons. Characters are always losing body parts. If they can't use a replacement limb, somebody else can and they'll probably pay well for it.

Your average village witch or reclusive wizard probably won't fashion magical prosthetic, but a large college or conference will probably have someone with the right tools and mindset.