A True Potential is the highest level of Elemental Powers accessible to an Elemental Master, tapped into through overcoming the emotional obstacles that are holding them back. When in use, the master's bodies glow, they are surrounded by the colors of their elements, and they can freely control and manipulate their elemental powers.
“You will not hurt my friends. There is nothing that will hold me back. I know who I am.”
— Zane, "Tick Tock"
Zane unlocks his True Potential in "Tick Tock," giving him the ability to levitate and harness his Ice powers as beams or explosions. Zane was able to unlock his True Potential upon discovering his past, learning that he was a robot who nonetheless had a loving father, and then confronting the Treehorn Queen in defense of his friends.
“Whatever happens next, just remember, you are the best you.”
— Nya, "Once Bitten, Twice Shy"
Jay unlocks his True Potential in "Once Bitten, Twice Shy," enabling him to fly, teleport short distances, travel through electrical currents, gain exceptional strength, and even allowing him to use the power of Wind for a brief moment. Jay was able to unlock his True Potential through discovering Nya's feelings for him, and realizing that he simply needs to be himself.
“Cole's found his True Potential. His relationship with his father must have been holding him back.”
— Zane, "The Royal Blacksmiths"
Cole unlocks his True Potential in "The Royal Blacksmiths," giving him increased strength, near indestructibility, and levitation. Cole was able to unlock his True Potential because his father respected him for who he was, not what he wanted him to be, strengthening their relationship.
“I knew when I had to make a choice. I wanted the Fangblade so badly, to prove I was good enough to become the Green Ninja. But then I figured it out. All of my training to become the best Ninja wasn't in preparation to become the Green Ninja. It was... to protect him.”
— Kai, after Zane asked him how he unlocked his True Potential, "The Green Ninja"
Kai unlocks his True Potential in "The Green Ninja," in this state, he is enveloped in a sphere of fire, granting him flight, and the ability to endure extreme heat. He is also able to protect others within this sphere. Kai was able to unlock his True Potential by realizing it was not his destiny to become the Green Ninja, but Lloyd's.
Lloyd unlocks his True Potential in "Rise of the Spinjitzu Master," becoming the Golden Ninja and Ultimate Spinjitzu Master. He had all of the abilities of the First Spinjitzu Master, including massive control over the four main elements, levitation, the ability to summon the Golden Dragon, and manifest Golden Power into a protective sphere and powerful blasts of energy. These powers allowed him to defeat the Overlord and purge Ninjago of evil. Lloyd stayed in this state constantly, until the Overlord later drained him of his Golden Power. Lloyd was able to unlock his True Potential at the Final Battle when he announced that a Ninja never quits and finally understood that it was his destiny to become the Ultimate Spinjitzu Master.
Nya unlocks her True Potential in "Curseworld, Part II." In this state, she was enveloped in a vortex of water and was able to summon an enormous wave to drown the Preeminent. Nya unlocked her True Potential by accepting her past failures and realizing that the possibility of failure should not stop her from continuing to try.
“As Wu had previously taught the Ninja, you too can unlock your True Potential, a dark potential. But to achieve it, you must overcome the one obstacle that has always stood in your way. The one person who has always held you back.”
Garmadon began to unlock his True Potential in the episode of the same name. After freeing Harumi and the rest of the Sons of Garmadon, Garmadon was told to unlock his True Potential by defeating Lloyd without holding back. By defeating Lloyd following their battle at Kryptarium Prison, Garmadon gains access to his true destructive powers and his dormant element of Creation, due to him being a descendent of Dragons. Later, Garmadon was also able to create a large Colossus being with both his Destruction and Creation powers.
However, in "Two Lies, One Truth," Harumi confirms to Garmadon his potential is not yet complete. To truly unlock it, rather than defeat him, he must end Lloyd's life. Garmadon came even closer to unlocking his full power when he fought Lloyd and Wu in the ninth season finale, "Green Destiny." Lloyd managed to prevent Garmadon from achieving this goal by refusing to engage in combat with him, causing him to weaken to the point of losing his power altogether. However, after sparring with the Ninja, Garmadon regained his powers and can use Creation when he activates his True Potential. In "Endings," Garmadon demonstrates that he can use his True Potential to transform into an Oni and greatly enhance his strength, speed, endurance, and powers.
“It appears Dragons go through a metamorphosis when they reach adulthood. They too have found their True Potential.”
In "Day of the Departed," Cole was brought to the brink of despair by Yang, who mocked him for being a forgotten ghost doomed to fade away. When the other Ninja arrives, Cole realizes that his friends will always be by his side, and with his hope regained, he unlocks the Earth Punch, a move that covers his arms in molten lava, and increases his strength tremendously.
Garmadon mentioned in "The Invitation" that all the Elemental Masters have already found their True Potential and mastered their powers. This meant at some point before their appearances, they overcame their fear and became true Elemental Masters.
Strangely, of the four original Ninja, Zane, Jay, and Cole all have blue glowing eyes when they unlock or use their True Potentials; Kai is the only Ninja to have red glowing eyes instead.
Considering Garmadon's True Potential gives him access to Creation, Wu's True Potential may give him access to his recessive element, Destruction.
As a result of Garmadon's True Potential, he was able to shape-shift into an Oni.
In the Ninjago Character Encyclopedia, it was called "full potential" instead.
When asked why the Ninja stopped using their True Potential powers, Tommy Andreasen explained that "True potential must be maintained." He had also said earlier that they may have lost the abilities once they gave their powers to Lloyd (in "Island of Darkness").
The Forbidden Spinjitzu, accessed by the Scrolls of Forbidden Spinjitzu, is stated to have power comparable to that of accessing a True Potential. Whether the scrolls truly unlock one's True Potential as long as they wield it or it simply grants them powers similar is unknown. Aside from Zane and Lloyd, when Wu, Garmadon, and the Ninja have held the scroll, they merely used the enhanced Spinjitzu and never used their Elemental Powers. Zane was able to defeat the Pyro-Vipers quickly by blanketing them in ice.
Regardless of whether it grants the wielder access to their True Potential, the Scroll's powers are shown to be so potent that Zane, as the Ice Emperor, corrupted by using it, was able to overpower Lloyd. Even with the latter's Golden Power lost, he was still the most powerful Ninja, due to having the Essence of Energy, indicating the Scroll could be even stronger than a True Potential.