General Kai

Kai is a supernatural yak who was the former brother-in-arms-turned-archenemy of Master Oogway, Po's second archenemy after Lord Shen and later, (upon his return to the mortal realm), he becomes a powerful evil Spirit Warrior. Thus, he can steal chi from Kung Fu warriors and turn them into Jade Zombies (or Jombies, as Monkey and Po call them). His scheme is to defeat every Kung Fu master and become all powerful. 500 years after his banishment to the Spirit Realm, Kai has grown much stronger in his power. In the Spirit Realm, he finds Oogway and challenges him to a rematch and he returns to the mortal world.