Fight One
Finn, Jake, Princess Bubblegum, Marceline, Ice King, and Flame Princess, and BMO
Vs
Aang, Katara, Toph, Zuko, Sokka, Suki, Momo, and Appa
Round 2
Vs
Korra
Mako
Bolin
Asami
Tenzin
Lin Beifong
Round 3
All of Ooo vs all of Avatar world, with a year of prep time.