The Toa Nuva were heroes gifted with greater strength, stronger armor, and greater control over their elemental powers than ordinary Toa possessed. Toa Nuva had the ability to use Kanohi Nuva, masks which allowed the wearer to share their power with those in close proximity. The only known means of transforming a Toa into a Toa Nuva was by exposure to energized protodermis. The only six Toa Nuva ever known to exist were Tahu Nuva, Pohatu Nuva, Onua Nuva, Lewa Nuva, Kopaka Nuva, and Gali Nuva, who were originally the Toa Mata. Their transformation made them more powerful than before and for a time threatened to shatter their unity. However, they were able to combine forces to defeat the Bohrok-Kal and the Rahkshi.
The strange energies of the protodermis transformed the Toa into the Toa Nuva, with new tools, new armor, and greater power than ever before.
As Toa Nuva, the Toa had greater power, and control over that power, than ever before.
After their transformation, the Toa Nuva discovered that they had greater control over their power than ever before.
The Toa Nuva's new adaptive armor adapted to any environment, making them ready for battle wherever they went. In the swamp of Karda Nui, its flying jets kept the Toa safely in the air above its terrible waters. The Toa weapons adapted to be Nynrah ghost blasters, capable of firing a burst of energy which could then be shaped and controlled by the mind of the Toa into any form. Like their armor, the Toa Nuva's masks also adapted to combat in the swamp, becoming more streamlined for flight.
There was a process that the Toa Nuva could have used to wake up Mata Nui without using the Ignika, but it would have been time-consuming. The Toa Nuva simply used the Ignika as a tool to do it faster.
Once out of Karda Nui, the Toa Nuva (except for Tahu Nuva) gained access to all of their other Kanohi Nuva again.
Compared to before, the Toa Nuva's armor and tools were better, and they were faster, more agile, and stronger.
Toa Nuva were not significantly stronger than a standard Toa physically, but they had better control over their elemental powers, better armor, and could share their mask powers.
The destiny of the Toa Nuva was to awaken Mata Nui. If they chose to sacrifice their Toa power after they accomplished this, they would become Turaga.
The Toa Nuva could only lose their powers if their symbols were in possession of someone besides themselves or the Matoran.
The Toa Nuva were equivalent in strength to the Piraka.
The Piraka were not necessarily stronger than the Toa Nuva, but they had the advantage of surprise and Brutaka on their side.
"Nuva" likely meant "new" in Matoran.