While there are many powerful artifacts and items in the show, such as:
* The Elements of Harmony: These powerful artifacts are the source of ultimate harmony and are used to defeat Discord and other villains.
* The Alicorn Amulet: This amulet is worn by Princess Celestia and Princess Luna and is a source of their alicorn magic.
There is no singular necklace that specifically grants ultimate magical powers. The concept of a single object granting ultimate power is not a common theme in My Little Pony.
The show often emphasizes the importance of teamwork, friendship, and the power of believing in oneself, rather than relying on magical artifacts for power.