Carrying the tradition that Pokemon X and Pokemon Y started, some Pokemon in Alpha Sapphire and Omega Ruby will be getting new Mega Evolutions. The transformation is now initiated by the Mega Bangle instead of the Mega Ring but it functions the same exact way.
Update 11/22/2014: Pokemon in Pokemon OR/AS that are holding their Mega Stone or knows a new move introduced in OR/AS cannot be traded or used in battle in Pokemon X/Y. Know more about the compatible versions in both games with our Compatibility page.
In a cave
Where do I get beedrills mega stone?