The player can obtain the Charizardite X by reaching Trainer Rank 26. It is also available on Week 23 of the event rotation.
The Charizardite X was also available as a prize during the Mega Charizard Competitive Stage. This Competitive Stage ran on the Nintendo 3DS version from February 23 to March 1, 2016; August 30 to September 6, 2016; August 2 to 8, 2017 and January 2 to 9, 2018. It ran on the Pokémon Shuffle Mobile from August 30 to September 6, 2016; August 2 to 8, 2017 and January 2 to 9, 2018.
The Charizardite X enables the following Mega Evolutions:
Erases Pokémon and disruptions around two spots you tap. Erases five tiles in a + shape surrounding each spot. Does not activate if the foe is defeated. Only gives 3 seconds to tap. Can erase fewer than 2.
Alain once owned a Charizardite X that he obtained from Lysandre along with his Mega Ring, giving it to his Charizard to wear 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 where it could be caught.
In Malamar Traps, X's Salamè was revealed to keep a Charizardite X hidden within 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.