The Thunder Rock (カミナリいし, Kaminari Ishi?) is an object from Final Fantasy Mystic Quest. It is retrieved by Benjamin and Reuben from Fireburg after Otto tells them that he can power up the Rainbow Bridge Machine with the rock, making it strong enough to project the Rainbow Road all the way to Spencer's Place. The heroes take it back to Windia and give it to Otto. Sure enough, his machine is able to extend the path as Otto believed, and the two heroes then cross it and use a Mega Grenade to release the water from the upper lake into the dried-up lake bellow.