Use ice or fire type pokemon
Flying, ice, fire psychic
ice dragon
It doesn't matter which order as long as you complete all three planets (jungle, fire, and ice). Fire is the hardest of the three.
Rock beat Ice types also Steel, Fire and Fighting types.
If you didnt already beat fire planet beat that. Or find the crystal rock thing.
By using Fire, Ice or Flying type moves.
fighting, fire, and rock.
fire types[sorry for the short answer] ^ I'll extend your answer then. Fire, Rock, Steel and Fighting.
beat the elite four 100 times to get fire, ice, and thunder punch all at once
make sure you have fire Pokemon with you and you will win easy
fire, ice, poison, flying, or bug types