I need to give you this insight on the broken mess known as Mega Rayquaza. Mega Rayquaza doesn't need a Mega Stone to Mega Evolve. It needs to learn Dragon Ascent, a flying type Close Combat, in order to do so. That means he can hold an item. What's the big deal about that? Well, he has the highest stats in the game: 105/180/100/180/100/115, with a total of 780. He is only weak to Dragon, Ice, Rock, and Fairy. AKA, you need him on your team, ASAP.