Pokemon X and Y Walkthrough: Tower of Mastery
The gigantic statue of Lucario welcomes you to the tower. Enter the door at the base of the statue to meet Korrina and the Mega Evolution guru. Tierno, Trevor, Shauna, and your rival eventually show up to hear what the guru has to say. He explains the ins and outs of Mega Evolution. Some Pokemon can temporarily evolve beyond what was previously known as their final evolution. These Pokemon can Mega Evolve only during battle and they return to their normal state once the battle ends. Some Mega Evolved Pokemon have improved stats and even have different types than their original form. Finally, all of this is unlocked through the connection between a Pokemon's Mega Stone and the Mega Ring. Unfortunately, the guru only has one ring to give away. It all comes down to a battle with your rival.
Korrina challenges you and the rest of the group to battle for the Rumble Badge back at her gym in Shalour City.