Sensei Yang is a recurring character in Ninjago: Masters of Spinjitzu and is the main antagonist of the Day of the Departed TV special.
At an unknown point in time, Yang invented the technique of Airjitzu and would later take several students under his teaching, he later discovered the Yin Blade that can make everything Immortal, while testing it on himself, he along with his students were converted into ghosts.
Yang was mentioned by Misako to be the creator of Airjitzu.
The Temple on Haunted Hill
During the Ninjas' stay at the Temple to locate the Scroll of Airjitzu, he threw many obstacles (the fears of the Ninja) at them to make them stuck in the Temple. Later, it's revealed that he tested the Ninja if they're worthy for the Airjitzu scroll. However, as the morning came and the curse on Yang's Temple started to take effect on the Ninja, Yang's other students showed themselves, revealing them to be chained up, as they were imprisoned by Yang. The Ninja then quickly fled to the entrance, not wanting to suffer the same fate as Yang's students. They manage to reach the entrance, but Cole dropped the scroll mid-way and thus had to go back in to retrieve it, which caused him to turn into a ghost, with Yang's laugh echoing from the Temple.
After his temple was torn out of Ninjago to help construct Djinjago, he left his temple to angrily confronted Nadakhan, claiming domain. However, the latter, unimpressed, promptly ordered Dogshank to shoot water at him and his students, forcing them to abandon the temple.
The Way Back
Yang's temple was strangely left still floating in the sky despite Jay's final wish. This may be due to Yang having "power" over his temple, being able to do many things with it.
Day of the Departed
Yang lures Cole into coming to the Temple of Airjitzu where he tricks Cole into opening a rift to the Departed Realm with the Yin Blade which releases several of the ninja's defeated enemies. He has his students subdue the earth ninja and contacts the villains telling them to return to Ninjago they must destroy one of the ninja to take their place in the living realm. Yang then reveals to Cole his plan of returning to Ninjago and with the ninja gone he would leave Cole to take his place as the master of the temple. Yang later uses the Yin Blade to open a large Rift in the sky and tries to use escape through it but Cole having escaped stops him. The two battle with Yang trying to demoralize Cole by stating his friends have forgotten him and is nearly successful in breaking the latter's will to fight but Cole's friends call out to him. With this the newly energized Cole finds the strength to fight back, he tells Yang he was the one that was alone while Yang states he has his "family" but Cole states they are captives. The two clash once more and Cole breaks the spell over Yang's students before directing them to the rift to be free of Yang's influence. Once they leave, Yang realizes he is truly alone and laments that he always failed revealing that he cursed himself to be remembered forever as he realized everyone would forget him. Understanding this, Cole manages to get through to Yang by telling him people would of remembered him due to him creating Airjitzu. He then tries to take Yang with him through the rift before it closes however, Yang notes the curse would require one of them to remain. He then tells Cole he will settle his "debts" and flings the earth ninja through the rift turning him back to a human. Afterwards the ninja make the restored Temple of Airjitzu their base with only Cole being aware of Yang's presence. While celebrating the next Day of the Departed, Cole states there are no more before he winks at Yang and the latter having come to terms with his fate of being a ghost winks back.