|“This clock was created to countdown to the Final Battle. Once one takes the Helmet of Shadows, the clock will start. But be warned, though he who wears the Helmet of Shadows can travel between the Islands at will, once it is removed, the countdown cannot be stopped.”|
|— The Overlord|
The Celestial Clock is a mechanical device that rests atop a high mountain on the Island of Darkness. It is a massive machine with a large clock at its core and several sphere-tipped metal arms rotating around it. It held the Helmet of Shadows until it was removed, then started counting down to the Final Battle.
After Lord Garmadon raised the Island of Darkness from the sea, The Overlord led him to the Celestial Clock and told him to take the Helmet of Shadows, which allowed the Celestial Clock to begin its countdown. The Overlord later told Lord Garmadon that their ultimate weapon would be ready just in time for the final battle, as dictated by the Celestial Clock. Garmadon then placed his old helmet in its place.
At the suggestion of Misako, the Ninja attempted to halt the countdown by stealing the Helmet of Shadows from Lord Garmadon and returning it to the Celestial Clock. Unfortunately, they were unable to find the Helmet's pedestal in time, replacing it moments after the countdown finally finished. The Celestial Clock proceeded to release beams of energy between the many spheres orbiting its core, eventually firing the ray straight into Lord Garmadon's camp. As the Overlord gloated about the imminent victory of darkness over light, the Garmatron began to take shape within the energy beam of the Celestial Clock.
Sometime later, Chen succeeded in taking a piece of the Celestial Clock and displaying it in his Hall of Fame.
Whilst touring Kai in his Hall of Fame in an attempt to sway the Fire Ninja to his side, Chen boasted over his possession of a gear from the Celestial Clock.