During a visit to Ninjago History Museum, Cole (who is still a ghost) realizes that he is starting to fade away and, after discovering the Yin Blade, decides to visit the floating Temple of Airjitzu to confront the ghost of Master Yang.
At the temple, Cole accidentally uses the Yin Blade to open a portal to the Departed Realm, thereby releasing the spirits of the ninjas' old enemies, which include Samukai, Kozu, Cryptor, Chen, and Morro, who are also joined by Pythor. The spirits possess their mannequins in Ninjago History Museum, which brings them to life. Cole is detained at the temple by Yang's ghost students. Yang then tells the villains that they can stay in Ninjago if they defeat each of the ninjas that defeated them. Yang seizes the Yin Blade from Cole and explains that he intends to use the blade to tear open the Rift of Return so that he can be revived. The ninja are under attack from their old revived enemies, but successfully defeat them one by one. In the meantime, Cole is forced to fight Yang's students as he follows Yang up to the temple roof. Yang uses Airjitzu in an attempt to reach the Rift, but Cole stops him and they fight.
When the ninja are reunited, they realize that they had almost forgotten about Cole. They return to the Temple of Airjitzu as Cole is battling Yang. Cole's spirit is bolstered at the sight of his friends and he shatters the Yin Blade. This frees Yang's students, who are able to cross through the Rift and become human again. Yang tells Cole that he wanted to be remembered, but Cole replies that he will be remembered as the creator of Airjitzu. They agree to cross through the Rift together, but during the ascent, Yang decides to stay at the temple to settle his debts and launches Cole into the Rift. The ninjas soon discover that Cole has returned, now in human form once more. They celebrate the return of their friend and decide to use the Temple of Airjitzu as their new base.