True Potential

A True Potential is the highest level of elemental power unlocked by the Ninja, tapped into through overcoming the emotional obstacles that are holding them back. When in use, the Ninja's bodies glow, they are surrounded by the colors of their elements, and they are able to more freely control and manipulate their elemental powers.

Zane's True Potential
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.

Zane was the first one to find his True Potential.

Jay's True Potential
Jay unlocks his True Potential in "Once Bitten, Twice Shy," enabling him to fly, teleport, travel through electrical currents, and gain exceptional strength. Jay was able to unlock his True Potential through discovering Nya's feelings for him, and realizing he simply needs to be himself.

Cole's True Potential
Cole unlocks his True Potential in "The Royal Blacksmiths," giving him incredible strength, 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.

Kai's True Potential
Kai unlocks his True Potential in "The Green Ninja"; in this state, he is enveloped in a sphere of Fire that can endure extreme heats, fly, invulnerability and protect others within it. Kai was able to unlock his True Potential by realizing it was not his destiny to become the Green Ninja, but Lloyd's.

Kai was the last to find his True Potential.

Similar Phenomena
In Day of The Great Devourer, when the Ninja's Dragons were revealed to have molted and merged into one entity during their time at the Spirit Coves, Zane likened the process to the Ninja unlocking their True Potential.

Later in Island of Darkness, after losing their Golden Weapons and discovering the Island of Darkness, the Ninja learned of a prophecy in Misako's scrolls that told of a ritual that would unlock their "true elemental powers." Upon enacting this ritual at the Temple of Light, the Ninja received their Elemental Blades and stronger powers, similar to when they unlocked their True Potentials.

During the final battle against the Overlord in Rise of the Spinjitzu Master, Lloyd unlocked his power as the Ultimate Spinjitzu Master, vastly enhancing his strength, turning his entire outfit gold, and enabling him to manipulate pure light energy to an impressive degree. Although it was never explicitly stated, it could be assumed that this form is the Green Ninja's version of True Potential. This is further supported by the "Golden Lloyd" minifigure found in two 2013 sets, which has an identical metallic sheen on the outfit and the head, similar to the other Ninja's NRG forms (which depict their True Potential forms).