So I got the idea, what if someone was terrified about the Firenation... that they, with the help of others, tried to create a new Avatar but.. they were stopped. The Child in question was blessed, a firebender child, with a fraction of the Essence of the Ocean Spirit, granting them Waterbending.
In one idea, the child is slaughtered and is reborn with Korra, and live during her life time... in another the child is about ten when Aang is found, and we see how they rebel again teh Firenation and such...
Either way, they would have immeasurable Water based powers, including the power to heal masses with water, influence the weather and more. They could, maybe, energy bend ( or at least have the potential) . They would share some charecteristics witht eh Avatar, but would not be the same. Many traits would be completely unique...
I also though of Azula, insane and evil as she is, try to do this to herself but dies and is reborn as the Ocean Avatar or whatever... and we see the ripples from that...
Another idea i had came from Buffy... when Aang dies in Ba Sing Sai a piece of his essence is reborn as a different being ( but only really gets reborn when Aang dies finally, as they are connected)... the child has two elements only, whatever their natural element is and one other that depends on their lineage... anyway they work along side or even against Korra...
Lastly, a child of a firebener born of supposed ( Not real but assumed) rape in the South Pole... the child develops a style of firebeding around Heat and Auras, and lives on their own for years since they are hated... they eventually join Zuko's ship in secret, only talking to Iroh ( who teaches them firebending in a more advanced way)before leaving to travel the world and realizing that everyone sucks, not just the water tribe who abused them...like a reverse Hama
