I don’t know if any of you guys have seen this but this is the strongest Sun and Moon theory I’ve seen so far. The theory goes like this:
The strange souvenir, which depicts a legendary which was highly regarded in a completely new region, not only protected that region but the entire Earth.
Zygarde created Xerneas and Yveltal to maintain Earth’s balance.
Zygarde is based on a serpent in Norse mythology, that wrapped itself around the Earth then bit onto it’s tail to hold the world in place. If it were to let go, the earth would fall apart. This parallels Zygarde’s role.
Team Flare’s true goal was to launch the ultimate weapon to gain the attention of Zygarde who would come to deal with the upset in balance. This is just like in the anime.
Zygarde is the third, Earth legendary in the Sun and Moon trio as well as the final member of the Mortality trio.
Zygarde’s name comes from “syzygy” which refers to the Sun, Earth and Moon.
Complete Zygarde’s markings represent, from left to right, Xerneas, the Moon legendary, the Earth, the Sun legendary and Yveltal.
There was a bit more in the video but this is the part that’s probably pretty accurate.