The Charizardite X (Japanese: リザードナイトX Lizardonite X) is a type of held item introduced in Generation VI. Along with Charizardite Y, it is one of the Mega Stones associated with Charizard.
If held by a Charizard (or is present in the player's Bag)PE, allows it to Mega Evolve into Mega Charizard X 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 X or remove a Charizardite X from Charizard.
If held by a Charizard, allows it to Mega Evolve into Mega Charizard X when it performs a Spectacular Talent during a Pokémon Contest Spectacular while its Trainer has a Key Stone. Charizard will remain a Mega Charizard X until the Talent Round ends.
Alain owns a Charizardite X that he obtained from Lysandre along with his Mega Ring. Alain's Charizard wears it around its neck. After realizing Lysandre's true intentions, and the error of his own ways, Alain disposed of the Charizardite X sometime before Till We Compete Again!, promising to start from a clean slate.
In File 2: Cubone, Mr. Fuji gave Red a Mega Stone and a Key Stone, although he did not tell Red what they truly were, merely saying that he would find out soon enough. In File 4: Charizard, during Red's battle against Mewtwo, one of the stones was revealed to be a Charizardite X from Kalos. Together, it and the Key Stone triggered Red's Charizard's Mega Evolution, allowing it to Mega Evolve into Mega Charizard X and weaken Mewtwo to a point whee it could be caught.
In Malamar Traps, X's Salamè was revealed to keep a Charizardite X hidden in his tail flame, explaining his habit of holding onto his tail. After evolving into Charizard, he became able to use the stone to Mega Evolve into Mega Charizard X.