Certain Pokemon in Kalos Region can turn into their mega evolved form when they are holding a certain Mega Evolution stone. Think of them as Eevee where if given a Fire Stone, it will evolve into Flareon, though in Mega Evolutions, they are temporary and will only apply in battle. Through the vast list of Pokemon that players will find in Kalos, several of them will have an opportunity to “mega-evolve” where their abilities, appearance, or even move sets will be different than their regular evolved form.
To let a certain Pokemon evolve into their mega evolution form, have them hold a certain stone and when in battle, simply choose the Transform option and they will evolve temporarily. This can be done after the third gym when you receive the Mega Ring.
Below are the list of Pokemon that can turn into their mega evolved form and the stones needed. The stones can be found throughout Kalos and can be traded with friends through locally, or the internet.
Mega Evolution Stones and the Pokemon
Charizardite X Stone (Pokemon X Only)
Charizardite Y Stone (Pokemon Y Only)
Mewtwonite X Stone (Pokemon X Only)
Mewtwonite Y Stone (Pokemon Y Only)
For more Pokemon XY Guides, check out our Pokemon X & Y Game Guide page.