If held by aGyarados (or is present in theplayer'sBagPE), the Gyaradosite allows it toMega Evolve into Mega Gyarados if itsTrainer has aKey Stone. A Trainer can only Mega Evolve one Pokémon per battle (or only have one Mega-Evolved Pokémon at any given momentZA).
As aMega Stone, it is unaffected by item-negating effects (such asEmbargo andKlutz). Item-manipulating effects (such asTrick andFling) cannot give or remove a Gyaradosite from Gyarados.
Outside of battle
If held by a Gyarados, the Gyaradosite allows it to Mega Evolve into Mega Gyarados when it performs aSpectacular Talent during aPokémon Contest Spectacular if its Trainer has a Key Stone. Gyarados will remain a Mega Gyarados until theTalent Round ends.
The player can obtain the Gyaradosite by completing thecompetitive stage available in Week 9 of the event rotation.
The Gyaradosite was also available as a prize during the Mega Gyaradoscompetitive stage. This competitive stage ran on both the Nintendo 3DS and Mobile versions from June 28 to July 5, 2016; January 31 to February 7, 2017; and June 27 to July 4, 2017.
The Gyaradosite enables the following Mega Evolutions:
Another Gyaradosite appeared inWhen Regions Collide!, where it was held byMisty'sGyarados. It didn't appear to be equipped on Gyarados, but rather, it appeared on its head crest right before Mega Evolving.
Lysandre owns a Gyaradosite, which first appeared inChespin Sows the Seeds of Change. AfterCelosia stoleKorrina'sKey Stone, it was fashioned into a Mega Ring for Lysandre, allowing him to use it and the Gyaradosite to Mega Evolve his Gyarados. Eventually,X stole the Key Stone back from him.
Merchandise
The Gyaradosite has been featured in several officially licensed merchandise.
Mega Ring System Gyaradosite
Gyarados, Mega Gyarados & Gyaradosite metal charm set
