Eye of Onyx

The Eye of Onyx is a black sphere, a enchanted piece of SandWing Treasure, with wings made from molded, beaten gold, and set on a chain of golden links. Due to its name it is almost certainly made from onyx.

Whoever holds the Eye of Onyx rules the Kingdom of Sand, as long as the current SandWings queen has died. Therefore, if Princess Blaze, Princess Blister or, Princess Burn were to have the eye they would've become queen and stopped the war as Princess Sunny did in The Brightest Night.