The Talismans of Transformation were dark side artifacts used by the Nightsisters of Dathomir. They allowed their wearer to take the shape of another creature.
The Talismans of Transformation were crafted on Dathomir by the Shamans of the Nightsisters. Those talismans possessed strange arcane powers that both Sith and Jedi scholars could not fully explain. In the form of gems set in rings or pendants, they allowed the wearer to take the appearance of an animal. They were thought to work through the power of the "Spirits", which probably were a mythological embodiment of the Force in the Dathomirian culture. According to Mother Talzin, the Spirits agreed to empower receptacles in the physical world, where their essence would sleep until summoned.
The magic ring of Sister Charal, the self-proclaimed Witch-Queen of Endor, was in fact one of these devices, known as the Talisman of the Raven. Charal had probably stolen the ring when she abandoned her clan over a standard century before the Battle of Endor. At the time of the Clone Wars, when Mother Talzin wrote her instructional manual Wild Power, she mentioned this missing talisman.
When Darth Sidious came in possession of Talzin's manual, he remarked that those talismans didn't seem very different from Sith amulets, yet none of their abilities had been successfully duplicated by a Sith alchemist.
- Book of Sith: Secrets from the Dark Side