Diancie is an event-only Pokemon, therefore it cannot be captured in the wild or any special place. It was an event in October 2014, which was held at local game stores, such as GameStop. It was a serial code event.
Xerneas, Yveltal, and Zygarde There is also Diancie, but it is an event pokemon. You get the choice of Articuno, Zapdos, and Moltres depending on your starter.
From October 27 to November 16, 2014 you can obtain a free download code for the Mythical Pokemon Diancie for Pokemon X and Y. If this event Diancie is then transferred to the upcoming Omega Ruby and Alpha Sapphire then another event will occur where players can obtain Diancie's Mega Stone.
A Rock/Fairy-type legendary Pokemon that you can only get through events. It was first introduced in Pokemon X and Y.
You can get Diancie either by trading with someone that has one or through an event by redeeming a serial-code obtained at participating stores.In the United States, you will be able to receive a Diancie serial code between October 27, 2014 and November 16, 2014 by going to a Gamestop store. In Europe, the distribution date is between 6 November, 2014 and 28 November, 2014, in various retailing stores depending on where you live. Japanese people that bought tickets to the movie Diancie and the Cocoon of Destruction also received a Diancie.
Mystery Gift is a special event based distribution Nintendo implemented in the Pokemon games ever since Pokemon Gold and Silver. Basically with Mystery Gift your able to obtain special pokemon being distributed by Nintendo during a certain period of time like when a Pokemon Movie is being released for example. In X and Y the events that have occurred or upcoming so far are: Pokeball Vivillon, Green Vivillon, Speed Boost Torchic, Pinsir/Heracross (depends on which version your playing), Pinsirite/Heracrossite (Gamestop promotion), Diancie (Japan), Celebi (Pokemon Bank), *Shiny Gengar (Gamestop), *Diancie (America). *Events marked with an Asterisk will be upcoming and have not been released yet.*
National Pink Pokemon Day :D ~x~
Diancie is an event-only Pokémon so it cannot be found in Pokémon X or Pokémon Y, you can only get it through special Nintendo events.In the United States, you will be able to receive a Diancie serial code between October 27, 2014 and November 16, 2014 by going to a Gamestop store. In Europe, the distribution date is between 6 November, 2014 and 28 November, 2014, in various retailing stores depending on where you live. Japanese people that bought tickets to the movie Diancie and the Cocoon of Destruction also received a Diancie.
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Probably only by event. We just have to wait for it.
Yes, it's Pokemon HeartGold, and Pokemon SoulSilver
It has already been released. You can get it at Pokecommunity.