Book 2 is coming to an end and that means Book 3. Now this is all speculation none of this is confirmed this is just what i would like to see in the next season.
1. The Dark Avatar
Now in the final episodes of Book 2 we see Korra's uncle morph with the evil spirit Vatoo (who if I may say is the baddest baddy in the Avatar universe so far) with them morphing with each other they become the Dark Avatar. Now that being said why not Vatoo morph with another bender I mean Ravaa does it every time an Avatar dies why can't Vatoo.
2. The return of Amon
Now this is a little far fetched but now that Korra can go to the spirit world at will why not some old foes pop up like the spirit of Amon and Tarlock, this would be very cool but as I said far fetched but speaking of old foes...
3. Fire Lord Ozie
Wouldn't we all like to see this Korra already ran into uncle Iroh in the spirit world why not Ozie? I'm just saying.
Tell me what you guys want to see in the next season in the comments below.