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.
Whilst it does not return as an item in Golden Sun: Dark Dawn, the Dancing Idol can be seen on top of Lady Uzume's tomb. If one uses the Spirit Sense Psynergy to talk to her spirit, the idol begins to dance from a previously inactive state. It then returns to being inactive when Lady Uzume stops speaking with you.
The Dancing Idol is having apparent and similar feature in Jomon Statuette known as Dogū.