The catalyst that belonged to the notorious Morgana le Fay is a silver ring with intricate yet simple design and a black gem embedded on it.
Morgana gained the possession of this ring sometime prior to starting the conflict against Merlin and his supporters Merlineans, presumably from Merlin himself. Although the ring was destroyed by Veronica Gorloisen who absorbed Morgana's spirit into her own body, its magic flows into the dark enchantress also, allowing her to use magic even as a disembodied spirit whose form comprised of electron dust in the final battle.
Powers and Abilities
The ring has all the powers as other standard magic rings. Interestingly, its powers endures and flows within Morgana le Fay's spirit after its owner got caught within Veronica's Human Fusion Spell, though it's unclear whether this trait being exclusive to this ring alone.