I must say, this variation of pattern was a stroke of genius from GameFreak's part. It really encourages people to trade across the world, pulling more people to the global online services. Also, it is mimicking the real-world hobby of butterfly collecting (though, without the business with pins and boards and such). At the start of Gen. VI, when it was first revealed, Vivillon appeared to be one of the generation's very few formulaic Pokémon, in this case the bog-standard Butterfree clone. GameFreak had got rid of a lot of other cliches, but the staple early-game "larva-becoming-a-butterfly-via-a-short-pupal-stage" Pokémon seemed to remain in the game. However, it turned out there was a surprise up GameFreak's sleeve after all. Well done, I must say. I think we can expect other event Vivillon to be released with unique patterns in the future.