Such a weird Pokemon this one, and so under-featured. It's similar to Giratina, in that it's a bizarre extra Legendary without much explanation, and Kyurem as well, but I think it's even less explained than that. We've seen Xerneas, Yveltal and Zygarde, but unlike the Creation Trio and the Tao Trio, these three aren't really given much linkage to each other. The only link between Xerneas and Yveltal is that one is life and one is death, but that doesn't really link much to Zygarde's dominion of 'order'. And Giratina and Kyurem are talked about in the earlier games in their generations. I don't even think Zygarde is mentioned by NPCs.
tl;dr - I can't wait for "Pokemon Z" so we can finally learn a bit more about this guy, and maybe how the three link up.
And I know I ranted in an unrelated way to your picture, sort of, so let me see... I like how you did his scales. Don't quite understand the point of the plants and I like his head.