Alicorn Amulet

The  Alicorn Amulet  is a  magical  amulet that is featured in the episode Magic Duel. According to a book that the main characters find in Twilight Sparkle 's  library, the Alicorn Amulet blesses the wearer with "untold powers". However, the more the bearer uses the amulet, the more it  corrupts  him or her. The book goes on to say that the amulet has an in-built magical lock that prevents any  pony  other than the bearer from taking it off. However even the amulet has its limits, as it cannot perform feats that are considered simply impossible, such as duplicating a target, making a pony play ten instruments at once, or changing a pony's sex.

Trivia

 * Zecora gave the Amulet to Star Swirl the Bearded so he can us his magic to remove the corruption so it can be used for good.