The Tower of Mastery has a major role in the understanding of the concept of Mega Evolution. In it, the player learns about the history of Mega Evolution from Korrina's grandfather, Gurkinn. After this, the player fights against Serena/Calem for the Mega Ring so that they can use Mega Evolution, but it is only obtained once Korrina is defeated at the Shalour Gym.
After obtaining the Rumble Badge, Korrina will be waiting at the top of the tower, where she will give the player the Mega Ring. She then challenges the player to a battle, which serves as a tutorial for Mega Evolution. The player is loaned one of Korrina's Lucario to use against Korrina and her other Lucario in a one-on-one battle. If the player does not Mega Evolve Lucario, Korrina will rebattle the player until they do. After the player has Mega Evolved Lucario in battle, the player can choose to take Lucario with them.
The player isn't allowed to access the tower's upper floors until they've beaten Korrina at her Gym.
According to Gurkinn, Tower of Mastery was built on this specific location due to it being the same place where his ancestor and his Lucario once found a Mega Stone and a Key Stone, resulting in the first known Mega Evolution.
The Tower of Mastery first appeared in Trevenant Pokes and Heracross Transforms, where it was attacked by Essentia and her Trevenant in an attempt to find out the secrets of Mega Evolution. Korrina and Gurkinn did their best to defend the tower, but eventually Gurkinn chose to activate the tower's self-destruct mechanism in order to protect its secrets. The tower was collapsed into ruins, allowing the secrets of Mega Evolution to remain hidden, although Gurkinn was sad that the secrets of a certain Pokémon were also lost in the tower's destruction.
In PS587, Blaine was revealed to be one of the people whom Gurkinn had taught Mega Evolution to at the Tower of Mastery.