Have you ever wondered how Pokemon are chosen for Mega Evolutions since they were announced last year for Pokemon X and Y? Well Junichi Masuda has shed some light on this idea and how Pokemon are chosen for this evolution, and to put it simply it is all about what Game Freak thinks fans will enjoy and on some occasions how Game Freak can further balance battles with new ideas. But it would be easier to read Masuda's words which you can find below.
We have a real variety of methods in terms of how we pick who gets Mega Evolutions. One of the methods is to look at the battle balance. We obviously monitor how players are playing the game through tournaments like Pokémon World Championships or even just battles online for the ratings and looking at the current environment we’ll see who we should give Mega Evolutions to in order to improve the balance or counter some of the existing favorites.
Other considerations include what fans are excited for, like which Pokémon they really want to see Mega Evolutions for, so we look at that and we introduce a few that fans are really going to enjoy. Other than that, from a story a perspective, like this time with Alpha Ruby and Omega Sapphire, we kind of explore the origins of Mega Evolutions, and in that story Rayquaza is really prominently featured. We look at the story as well to see which Pokémon need Mega Evolutions there. And then it’s up to the designers to see which ones they really want to work on. So it’s a lot of considerations we have when we determine mega evolution Pokémon.