I completed the Pok?dex for the first time in all my years of being a Pok?mon player, starting back in 1996 with Red & Blue, in Kalos. I really wanted to do so because, for as easy as X & Y were, Generation 6 also gave us the new non-sprite Pok?mon models, great new aspects to the breeding mechanics, the return of the Shiny Charm introduced in Black 2/White 2, and Super Training which made EV training team members faster and easier than ever before. Expanding upon the Shiny Charm point, it gave me the opportunity to have an increased chance of breeding shinies not only for Omega Ruby & Alpha Sapphire but also for the later games in the series as well, which I have done a few times since.
Thankfully between some Generation III GBA carts of Ruby, Emerald, Fire Red, and Leaf Green, in combination with Platinum, HeartGold, SoulSilver, Black, White, Black 2, and White 2 I was able to scrounge up every last Pok?mon from the previous generations and transferred them up. It doesn't take as long as you might expect for as many Pok?mon as there are.
I went the route of creating a living Pok?dex, which means I have one of each and every Pok?mon gathered up together in the PC. I ordered them mostly by type and then threw all the Legendaries and Mythics in their own boxes.
I still need to spread my living Pok?dex from my one 3DS to the other. For context, I tend to play one version of Pok?mon (for example, Alpha Sapphire) on one 3DS and then play the other corresponding version (in this example's case, Omega Ruby) on the other. I do this for trading purposes. Once I get around to doing that, which I've been lazy on because that much back and forth trading is a big undertaking, I will need to transfer them up to Sun & Moon and Ultra Sun & Ultra Moon.