Helmet of Shadows

The Helmet of Shadows is a piece of headgear. It gives the wearer control over the Stone Army, and served as the seal for the Celestial Clock. The helmet was likely created by The Overlord, who gave it to Lord Garmadon to control the Stone Army. After the Overlord betrayed Garmadon and possessed his body, the helmet was abandoned in Ninjago City before being claimed by Dareth, who put it on and gained control of the Stone Army. Dareth commanded the armored warriors to attack the Overlord, though following his defeat they were ultimately destroyed. Shortly after, the helmet was stored away in the Ninjago Museum of History.

When Kozu and several Stone Warriors were resurrected on the Day of the Departed, Dareth ran into the museum and found the helmet, putting it on once more and regaining control of the Stone Warriors. Dareth commanded them to beat up Kozu, which they did, returning his soul to the Departed Realm.

The Day Ninjago Stood Still
When Lord Garmadon arrived on the Island of Darkness, the Overlord guided him to the Celestial Clock and encouraged him to take the Helmet of Shadows, but warns that once the helmet is removed, the clock cannot be stopped unless the Helmet is put back on. When Lord Garmadon put the helmet on his head, the hands of the Celestial Clock began moving once again, and the Overlord explained the significance of the artifacts to Lord Garmadon.

The Last Hope
Seeking a way to stop the final battle, Misako note that the scrolls say nothing about Celestial Clock being halted, but is led to believe that the countdown will stop if the Helmet of Shadows was returned to its pedestal. Sneaking into Garmadon's camp as a prisoner "captured" by Stone Warriors, which are actually the Ninja in disguise, Misako managed to convince Garmadon to remove the helmet long enough to steal it and make her escape in the Power Drill. As the Stone Army gave chase, Jay considered wearing the helmet, but was discouraged by the others, who suspected that its dark powers would corrupt any non-evil wearer.

When the Ninja reached the Celestial Clock, they searched for the helmet's pedestal. Unfamiliar with the clock's design, they were delayed long enough for General Kozu to arrive and reclaim the helmet. It changed hands repeatedly in the resulting scuffle, only for Misako to finally spot the pedestal. Unfortunately, she replaced the helmet a second too late to stop the countdown, forcing the Ninja to fall back as the Stone Army kidnapped Nya.

Return of the Overlord
The Stone Army returned the Helmet of Shadows to Lord Garmadon, along with the captured Nya. Garmadon was wearing the Helmet once again when he began piloting the Garmatron to attack Ninjago. When the Overlord possessed Garmadon's body, he continued to wear the Helmet.

Rise of the Spinjitzu Master
The Helmet of Shadows fell from the Overlord's head during his metamorphosis into his true form, and the villain left it in the streets of Ninjago City. This would prove fortunate for the heroes, as the Helmet would be donned by Dareth, and Misako was able to explain its function in time for the self-proclaimed "Brown Ninja" to save the Ninja from the Stone Army. Dareth then used his new headgear to send the Stone Army against the Overlord, buying time for the Ninja to begin ascending the dark dragon's tower.

At some point, the helmet wound up stored away in the Ninjago Museum of History, though it wasn't actually put on display.

Day of the Departed
On the Day of the Departed, the people of Ninjago commemorated their fallen ancestors and spent time with their families. The Royal Blacksmiths put on a performance, during which the four members each wore a replica of the Helmet of Shadows, in commemoration of the final battle.

At the time of the performance, several of the Ninjas' old enemies were resurrected, including Kozu and several Stone Warriors. Kozu confronted Dareth, who he held responsible for the second defeat of The Overlord. As Dareth ran into the museum, he found the Helmet of Shadows and once again used it to control the Stone Warriors, who turned on Kozu and beat him up. As a result, Kozu's spirit was sent back to the Departed Realm.