Following the reveal of Diancie’s event in February, hackers have now uncovered a hidden Hoopa event in X and Y‘s coding. It is activated when you have a special Hoopa in your party and talk to a man in the Parfum Palace Library.
Hoopa Event in X and Y:
“The Pokémon called Hoopa is linked to many of the unexplained supernatural events that have occurred in this world. My search for Hoopa has led me to this library.”
“No way! Could that be the Mythical Pokémon Hoopa that you have there with you?” Options: Yes | No
No: “Oh, I was mistaken? Sorry about that…”
Yes: “Whoaaa! I can’t believe it’s true! See, I travel around the world, trying to solve its many mysteries. I’ve been researching supernatural events that have occurred over the last 100 years. One thing I’ve found is that the Mythical Pokémon Hoopa is connected to many of these strange events! I’ve also managed to come across some information about the mysterious power that Hoopa appears to wield. So, without further ado, I’d like to share my findings with you! After all, you’re actually traveling with Hoopa–the very subject of my research!” Options: Its mysterious rings | The secret of its lair | Its deeds and exploits | Nothing
Its mysterious rings: “It’s said that Hoopa can use the power of the three rings it adorns itself with to move objects about as it pleases… That’s not all! I’ve also heard that when Hoopa unleashes its full power, the size of the rings can grow up to multiple miles in length! With such massive rings, apparently it can transport even entire islands!”
The secret of its lair: “It’s said that Hoopa’s lair is overflowing with the objects and treasures it nabbed over the years, claiming them for its own. Rumor has it that there are mountains of gold and silver treasures that it took from ancient kings and wealthy land barons. I hear that Hoopa’s lair is in an oasis in the desert, but no one’s been able to find the place!”
Its deeds and exploits: “There’s a tale about an organization that tried to manipulate Hoopa’s power for their own benefit. After a while, certain objects that belonged to the organization mysteriously began to disappear. Everything from weapons and vehicles to money… It all began to vanish one by one. The organization got scared and decided to hole up inside of their headquarters. Once they did, things stopped disappearing! Just like that! Relieved that it was finally over, the organization finally decided to step outside. It was then that they discovered their headquarters had been transported wholesale to somewhere in the middle of a desert! Terrified of what they had unleashed, the organization promptly disbanded.”
“Whether Hoopa becomes a trustworthy partner or ends up bringing about great misfortune depends entirely on the Trainer. I hope you don’t forget that. I think Hoopa’ll turn out right as rain with you at its side, though! You look like a Trainer who knows how to take care of his Pokémon and treat ’em right. Well, I hope you end up having lots of fine adventures with Hoopa! Have fun!”
We don't know when the event will be yet though so you will have to be patient.
Source: Hoopa Event