Well, Cynthia (the champion) has Spiritomb, Roserade, Garshomp, Gastrodon, Lucario, and Milotic. I chose Infernape, Roserade, Luxray, Staraptor, and Gastrodon.
beat the elite four and the champion.
You need to beat the elite four and then beat the Pokemon league champion
Defeat the Champion in the Elite Four.
Beat them and the champion
You have to catch at least 60 Pokemon and you have to beat the elite four including your rivalyou get it from oak after you beat the elite four and the elite four champion
train
Beat the Elite four and the Champion.
Beat all the elite four and there champion
beat the elite four and shes the champion
you have to beat the elite four plus the champion
Yes, you have to beat the Elite Four Champion before you can get Mewtwo, because there is a man standing outside the cave in Cerulean City, blocking the entrance, and he will only disappear if you beat the Elite Four Champion. Since Mewtwo is in the cave in Cerulean City, you have to beat the Elite Four Champion to even get into the cave where Mewtwo resides.
beat the elite four and become champion