Dancing Idol

The Dancing Idol is a Rare item in Golden Sun: The Lost Age. It is found at the peak of the exterior of Gaia Rock, invisible on top of a white pedestal (cast Reveal to see and take it). It is used in the interior portion of Gaia Rock by placing it on copies of the same style of altar to open paths and create beams of sunlight that will lower the difficulty of the Serpent boss fight in the end of the dungeon.

Afterwards, give this to Uzume in Izumo and she will give you a Mars Djinni.