I like the small improvements, however when you compare it to Chespin's model in-game (ORAS) the bottom part of it's body (just above the feet) look slightly more round, while I feel here it doesn't look the same, haha. ^_^
Also, about that Zygarde sprite: No offense, but the positioning of that sprite isn't the best. It's based off Xous54's unofficial Zygarde art, and it's not really right for a battle. It's looking straight ahead, not at your Pokémon. I understand that it must be really hard to sprite Zygarde, but I feel like a sprite like this would be better: