(Inspired on the story with the same title, but did small changes to the rules)
Thousands of years ago an evil wizard managed to create his greatest invention, an amulet capable of shapeshifting its wearer into anything, from animals and different people to inanimate things. He used it for his twisted desires such as haunting villages as a dragon, seducing and manipulating people as attractive women or devouring his enemies as a giant frog. Many mages realised the danger the amulet was for the entire world in those wrong hands, so they united and were successful in trapping him, even though they couldn't destroy the amulet they set a permanent seal that emptied its power. The wizard managed to escape but now with a useless amulet.
In his secret tower he could do nothing but release his anger, his life dedicated to his invention was burned down in an instant, but in a desperate attempt he did a radical change to the amulet. The reason it couldn't work anymore was that it ran out of power permanently, so what if the source of power was external? He thought. Then he came with the ultimate solution, he imbued the amulet with his own last source of magic but that wouldn't be enough for shapeshifting into anything, instead that magic would let the wearer turn other people... Into their body parts.
He maniacally laughed testing his new development, he wanted to transform himself into a centaur, so he kidnapped a victim and turned them into his lower horse part, being capable of turning himself back to normal and "storing" the person's soul into the amulet to use that transformation later. He kept doing the same for days, trapping various people into his tower to fuel his transformations, if he wanted to turn into a dragon again he would need to turn some into his dragon legs, other into a tail, other into his torso and one into his dragon head, with him remaining in total control of course, but the victims could experience the whole moment capable of feel and see, being able to talk if he allowed that.
But unfortunately for him, he was once again defeated and all his victims were released from the amulet. The wizard was executed and the amulet was kept hidden while being studied. The ones that investigated about its properties came to a couple of conclusions:
- As previously stated, the amulet wouldn't let to transform the wearer by itself but by turning others into their body parts. For example if the wearer wanted to have the arm of a werewolf they would need someone to merge with their arm to transform into a werewolf arm.
- The wearer needs to be in physical contact with their target to transform them into their part.
- The wearer can turn themselves back to normal, making the people turned into their body parts transfer their consciousness and soul to the amulet, in that state the wearer can decide to free them or keep them trapped.
- The amulet respects the exchange of equivalent mass, this means that if the wearer wanted to turn into a giant sized creature he would need more than one person for each body part, like turning many people into a single leg, many people into a single arm and so on for the rest of the body. At the same time if the mass of a single person is enough the wearer could turn then into more than one body part. For example if they targeted a tall person they could turn them into both of their legs if the mass is enough or making a single body part bigger with the extra mass.
- The wearer can touch someone and trap them in the amulet to use them into a body part later instead of immediately transforming them.
- The wearer can turn people into extra body parts, not necessarily fuse with their already existing ones, like turning them into an extra leg, or an extra breast.
- The wearer can choose the degree of the transformation of their target, like if they turned them into their lizard tail they could decide if they kept they head, arms or torso, or deciding to fully turn them into a lizard tail. This factor can be changed at any time unlike of turning them into a different type of body part.
- The wearer is in total control of their transformed body parts by default unless they want to give them control.
- The wearer can choose if the transformed people into their body parts keep their senses or choose what senses they will have.
- The wearer can use the soul of a person they trapped in the amulet to turn into various body parts in different times. For example trapping a person and transform them into their pair of wings but later into a tail.
- The amulet does the anatomical changes automatically when the merge occurs, but the wearer can specify changes if desired, such as transforming a person into their tail with a mouth and connecting them with their stomach, fuse a part with their reproductive system and many other cases.
- The amulet has a cooldown time after transforming someone into a body part, having to wait (presumably a couple of hours) before transforming someone more.
It seems that the more the amulet takes the stronger the magic becomes, capable of merging with people around them with no contact and other unknown abilities that could result into chaos.
Now in the present the story about the amulet became a legend and ended in a mysterious shop, unknown for anyone of its true powers. Until one day, the customer that bought it appeared.