In the last film, Po harnesses his inner Chi and becomes powerful enough defeat even a spiritual foe. The bar is set so high that what kind of villian would or could be used in the next few Kung Fu films. Well what if instead of a main villain that is predictable and would now be a piece of cake for Po, what if something happened that turned those he fought to protect, against him. What if Po had to fight his side, his own kind, the ones he loved. I know it would be a gut wrenching event but it could at the same time be a fresh idea needed instead of the same old.