Mega Evolution allows specific Pokemon to temporarily evolve into stronger evolutionary forms. The Mega Evolved Pokemon will remain in the new evolutionary stage for eight hours. Fainting in battle will not cause the Pokemon to revert to its previous form.
To Mega Evolve a Pokemon, Mega Energy for that species of Pokemon must be gathered. The Mega Energy amount will be listed on the Pokemon’s summary page, and the amount of Mega Energy needed to evolve will be in the “Mega Evolve” option below the “Power Up” option.