Nintendo says about 90 million Pokémon trades have been made via the GTS in Pokémon X and Y. Once we collectively hit 100 million trades, the new Fancy Pattern Vivillon will be attainable through a special distribution event worldwide. So get to trading!
If the design looks familiar, there's a reason why -- two new Vivillon patterns were discovered late last year, and the Fancy Pattern is one of them. The other features a Pokéball-themed design and will be distributed next month at the Paris Pokémon Center.
I "caught 'em all" earlier this year once the Pokémon Bank went online but haven't seriously attempted to collect every type of Vivillon. Seems like a daunting, frustrating process. That said, this goal is a great incentive for me to get back online and Wonder Trade away some of the harder-to-obtain Pokémon. Doing so brings me much joy.