If held by a Lucario, the Lucarionite Z allows it to Mega Evolve into Mega Lucario Z if its Trainer has a Key Stone. A Trainer can only have one Mega-Evolved Pokémon at any given moment.
In HZ131, Roy was given a Lucarionite Z by Master Mayonnaise, but didn't manage to Mega Evolve his Lucario with it at first, which Master Mayonnaise attributed to a lack of mastery of Lucario's true aura power. In the following episode, the Lucarionite Z was used successfully to Mega Evolve Lucario.
