If held by a Charizard (or is present in the player's Bag)PE, allows it to Mega Evolve into Mega Charizard Y if its Trainer has a Key Stone. Each Trainer can only Mega Evolve one Pokémon per battle.
Unaffected by item negating effects (such as Embargo and Klutz). Item manipulating effects (such as Trick and Fling) cannot give Charizard a Charizardite Y or remove a Charizardite Y from Charizard.
Outside of battle
If held by a Charizard, allows it to Mega Evolve into Mega Charizard Y when it performs a Spectacular Talent during a Pokémon Contest Spectacular while its Trainer has a Key Stone. Charizard will remain a Mega Charizard Y until the Talent Round ends.
The player can obtain the Charizardite Y by reaching Trainer Rank 7 or finishing Mission Card 8.
The Charizardite Y was also available as a prize during the Mega Charizard competitive stage. This competitive stage ran on both versions the 3DS and Mobile from September 18 to 28, 2015 and March 8 to 15, 2016.
The Charizardite Y enables the following Mega Evolutions:
In A League of His Own!, Trevor was revealed to have obtained a Charizardite Y before the events of the episode. His Charizard wears the Mega Stone on a ring around its tail.