X and Y, will feature "mega evolutions," according to a translation of a recent CoroCoro Japanese magazine by Serebii.
The translation lists a number of evolved Pokemon accessible in the upcoming games, along with their abilities: MegaBlaziken (Speed Boost), MegaAbsol (Magic Bounce), MegaMawile (Huge Power), MegaMewtwo (Insomnia), MegaLucario (Adaptability) and MegaAmpharos (Mold Breaker). Serebii notes that Mawile and its mega form are Steel and Fairy types as well.
MegaMewtwo was first revealed for Pokemon X and Y in April, and a video later showed its evolution from Mewtwo itself. We're going to miss calling it Mewtwo With a Handle, honestly.