In the core series games
If held by a Diancie, allows it to Mega Evolve into Mega Diancie 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 Diancie a Diancite or remove a Diancite from Diancie.
Outside of battle
If held by a Diancie, allows it to Mega Evolve into Mega Diancie when it performs a Spectacular Talent during a Pokémon Contest Spectacular while its Trainer has a Key Stone. Diancie will remain a Mega Diancie until the Talent Round ends.
Pokémon holding Diancite in Pokémon Omega Ruby and Alpha Sapphire cannot be traded to Pokémon X and Y.
|One of a variety of mysterious Mega Stones. Have Diancie hold it, and this stone will enable it to Mega Evolve during battle.
In spin-off games
In the manga
In other languages