Ok. This is a random theory I had.
This blog post contains spoilers from the season finale of Korra.
You know how Mako was able to resist Amon's bloodbending and shoot lighting at him? ALSO, how he is a champion Pro-bender and able to lightingbend and what...he is only 18? He must have a REALLY powerful bloodline...including an Avatar or something...
Maybe descended from Azula? Or Zuko. Then he would have a beast firebender like OZAI and an Avatar bloodline. And if he was from Azula...oh gosh. I best her kids are AMAZING firebenders... :P
What do you guys think?