|“He also says they have lost many warriors down the Mouth of Eternal Shadows just to obtain this one piece.”|
|— Kozu to Lord Garmadon in "Island of Darkness"|
The Mount of Eternal Shadows is the hideout of the Stone Army, Garmadon, and the Overlord on the Dark Island. The slopes of the mountain are where Dark Matter was harvested, and the Celestial Clock was found on its summit.
After raising the Island of Darkness from the sea, Lord Garmadon was told to climb the Mount of Eternal Shadows by the Overlord. When he reached the summit, he found the Celestial Clock and donned the Helmet of Shadows, setting the clock into motion.
At the mountain's summit, Garmadon berates the Overlord's Stone Army. The Overlord then tells him that Garmadon will rule over Ninjago once the Celestial Clock finishes its countdown.
The Ninja brought the Helmet of Shadows to the Celestial Clock to put it back on its perch. They were a second too late, and the Horns of Destruction marks the beginning of the battle.
The Ninja, Wu, Misako, and Dr. Julien infiltrated Lord Garmadon's camp. However, they discovered no sight of Garmadon and spotted tire tracks headed out near the coast.