Ursula's necklace is a magical item owned by said Sea Witch and it seems like it only works for those related to her by blood. Uma wears the gold nautilus shell around her neck via a golden chain.
- enabling shape-shifting
- storing other's voices
- hypnosis/controlling others
- Giving the owner the magical ability to cast spells
It once held Ariel's angelic singing voice.
In Descendants 3, Uma used it to hold Hades' Ember from Mal.
In Descendants 2, Uma uses it to grow tentacles to look as threatening as her mother.
In Under the Sea, the necklace played a major role. It was first seen glowing around Dizzy's neck, and it allowed Uma to talk to Mal through controlling Dizzy, Harry, and Gil.
In Descendants 3, Uma uses the necklace to give her the power and ability to cast spells, much like her mother, especially when converging with Mal and her powers.