Princess Bubblegum's crown

Princess Bubblegum's crown is a golden circlet with an inlaid turquoise jewel at the pinnacle. The crown and it's gem are important to her, considering she protects it well and is rarely seen without it. The crown has magic properties that were able to protect her from the Lich's mind-controlling powers in "Mortal Folly." In "Princess Cookie," Princess Cookie wanted the crown badly and took hostages in order to get it. In "The Lich" the turqoise jewel on the crown is revealed to be one of nine needed to unlock the Enchiridion's powers.

Trivia

 * Turtle Princess, Embryo Princess, and Slime Princess have the same kind of crown.