Guys my dad works at Nintendo and he taught me that if you beat the Elite 4 100 times with just a team of Venusaur, Blastoise, and Charizard, then Professor Oak will show up and say "WOW I NEVER THOUGHT YOU AND YOUR POKEMON WOULD BE THIS CLOSE" and he'll give you an item called a Mega Evolver which you can use to make them evolve into new pokemon that are stronger than Mewtwo