During battle, the player can use their Mega Ring to Mega Evolve a Pokémon if it is holding the correct Mega Stone before it attacks. Mega Stones only affect Pokémon during battles, and Pokémon will revert back to their basic form once the battle has ended. All Pokémon that can undergo Mega Evolution have an equivalent Mega Stone that is named after them.
Mega Stones cannot be transferred to or from the correct holder: Thief and Covet do not take the Mega Stone, Knock Off does not remove the Mega Stone, Trick and Switcheroo fail, Fling and Bestow fail, and Symbiosis does not activate. Embargo and Magic Room also cannot prevent the use of Mega Stones to Mega Evolve Pokémon. Mega Stones are not consumed upon use, but only one Mega Stone can be used per battle.
All Mega Stones not directly given or sold to the player can only be found between 8 and 8:59 p.m. after Professor Sycamore has upgraded the player's Mega Ring to detect them. These Mega Stones do not appear as item balls in the overworld; rather, they are "hidden" items denoted by sparkles around their locations.
The stone for Blaziken, the Blazikenite, cannot be found through normal gameplay within X and Y. However, it can be obtained via special distributions and trading.
In the anime, Pokémon wear Mega Stones using equipment similar to that which their Trainers use to hold their Key Stones. The equipment disappears while the Pokémon is in its Mega Evolved state.
Mega Stones were first mentioned in Lumiose City Pursuit!, where Professor Sycamore told Ash that a "special stone" is required to trigger Mega Evolution, referring to Mega Stones.
Mega Stones made their first physical appearance in Mega Evolution Special I. The seen Mega Stones were Alain's Charizardite X, Astrid's Absolite, Remo's Garchompite, Siebold's Blastoisinite, and an unknown orange Mega Stone found by Alain from ancient ruins. In addition, a Lucarionite was seen in a painting shown to Alain by Professor Sycamore in a flashback, featuring the first ever Mega Evolution.
Diantha's Gardevoir's Gardevoirite appeared in The Bonds of Evolution!. The Embrace Pokémon was shown carrying its Mega Stone in a necklace around its neck.
A Lucarionite made an appearance in The Cave of Trials!, where it was found by Korrina in a cave near Geosenge Town. After battling a Blaziken guarding the Lucarionite—which was afterwards revealed to belong to Korrina's grandfather, Gurkinn—Korrina obtained the Mega Stone and used it to Mega Evolve her Lucario. The "raw" Lucarionite was later set in an armband by McGinty, allowing Lucario to wear the Mega Stone.
Another Lucarionite appeared in The Aura Storm! under the ownership of Gurkinn. Much like Korrina's Lucario, Gurkinn's Lucario also wears its Lucarionite in an armband on its left wrist.
In the Pokémon Origins episode File 2 - Cubone, Mr. Fuji gave Red a Mega Stone and a Key Stone, although he did not tell Red what they truly were, 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 enough to be caught.
Diantha's Gardevoir has been shown wearing its Gardevoirite around its head.
Lysandre owns a Gyaradosite for his Gyarados but is currently unable to Mega Evolve it.
Clemont has an Electrike which evolved into a Manectric searching for its Mega Stone, which it eventually joined X's team after a Team Flare Grunt ambushed the group and stole the Manectite.
Artwork
The following is a gallery of Mega Stone artwork as seen on the Pokémon Global Link.
Abomasite
Absolite
Aerodactylite
Aggronite
Alakazite
Ampharosite
Banettite
Blastoisinite
Blazikenite
Charizardite X
Charizardite Y
Garchompite
Gardevoirite
Gengarite
Gyaradosite
Heracronite
Houndoominite
Kangaskhanite
Lucarionite
Manectite
Mawilite
Medichamite
Mewtwonite X
Mewtwonite Y
Pinsirite
Scizorite
Tyranitarite
Venusaurite
Trivia
The Aggronite and Houndoominite are only obtainable in Pokémon Y, despite Aron, Houndour and their evolutions being exclusive to Pokémon X.
The Tyranitarite and Manectite are only obtainable in Pokemon X, despite Larvitar, Electrike and their evolutions (excluding the Friend Safari) being exclusive to Pokemon Y