Round 1: Zuko and Azula as of "The Crossroads of Destiny" Vs. The Fire Ferrets. Korra can only waterbend. Fight is in the Pro-Bending arena
Round 2: Zuko and Azula as of "Sozin's Comet", which means Azula is insane and bloodlusted. Korra may bend all three elements.
Round 3: Same as Round 1, only Ty Lee and Mai join Zuko and Azula. Korra may waterbend and firebend, but not earthbend.