Breathing Prosthetics

Breathing prosthetics are expensive fake limbs that move with a will of their own.

Description

Breathing prosthetics are made to replace limbs that have been lost in either battle or surgery. They are usually made out of a fine, dark brown wood, but some have been made out of metal as well. They are very difficult to make, usually requiring 500gp and a week of operation. This means that only adventurers and wealthy nobles are ever seen with breathing prosthetics.
The prosthetics have a mind of their own. They are aware of their surroundings, and animate just as a normal hand or leg would, but the wielder has no control over their fake limb. Sometimes the prosthetics develop testy personalities, and they refuse to cooperate with their owners. In order for a breathing prosthetic to work, it must be taken care of by the wielder, and it must develop a bond over time.

Creation/Discovery

Breathing prosthetics have been around for a while, but they've only just recently become utilized on a wide scale. The first breathing prosthetics were created by the gnomes of Grapplecob. Tiny Tylithi created the first breathing prosthetic limb for for her brother. This was a couple hundred years ago, but the gnomes' secretive dwellings made it very difficult for the news to spread. 
Eventually, a tiefling researcher named Oziron found Grapplecob during his travels. He convinced a gnomish elder to travel with him into Fastelan to teach the council how to create breathing prosthetics. The first breathing prosthetic to be created outside of Grapplecob was made in 489. The prosthetics still spark conversations just about everywhere they are found.

 Famous Prosthetic Cases

Kett's Arm

Kett Zipoff runs a very grungy novelty hotel/casino in Celesta called The Metallican. In a blind act of publicity, Kett cut his own arm off, knowing that he could replace it with a metal one. You see, Kett was all about metal. He walks around with chains tied around his waist, and the hosts the most wild concerts in all of Distotia. 
Immediately after getting his metal arm, he taught it how to flip people off. Now it does this compulsively. Kett wouldn't have it any other way. He does, however, always carry fire starter on him, just in case he needs to burn his arm for disciplinary reasons. The hand also (of course) is insanely good at guitar.

Dalius's Legs

King Dalius the V lost his legs in a battle against the Kylans. For five years, he ruled with no legs. One day, he stood again, albeit with a cane. Dalius chose to hide his fake legs, and he instead pushed the narrative that he grew them back himself. He uses the cane in order to direct the prosthetics, as he can't control them himself.

The Automaton Heart

This is a gnomish myth. The story goes that one of the elders had died of a tragic heart failure, and in order to resurrect him, Tylithi replaced his heart with a crystal breathing prosthetic. Rumor has it that the heart is all-knowing, and whenever the elder is about to make a wrong decision, the heart will skip a beat to redirect them. There is no proof for this story, but it's interesting food for thought.