S1 E1 Rabbit Face
Kuzco faces his first threat of losing his position as Emperor when he struggles in P.E. and his teacher threatens to flunk him if he can't win a race with Kronk. However, Principal Amzy (who is really Yzma) tells Kronk to turn Kuzco into a turtle so he has no chance of beating Kronk, but instead, Kronk gives Kuzco the wrong potion and he ends up as a rabbit.