It's being distributed in celebration of a new online Pokémon store
I didn't get into collecting all of the uniquely-patterned Vivillons in Pokemon X/Y but I did quite like that one with the Poké Ball design that was given out earlier this year in France. (And I don't think it was a simple case of wanting what you cannot have.)
Thankfully, we'll have our chance: it's being distributed via the Internet now through August 12. This Vivillon is level 12 and knows Stun Spore, Gust, Light Screen, and Struggle Bug.
What's the special occasion for the giveaway? The Pokémon Company has launched a new online store called Pokémon Center that has t-shirts, hats, plush toys, cards, and more for sale.