From "How Odin Lost His Eye," a version of a Norse tale:
Now, think with me of the Kalos legendaries.In those days, folk say, there was a mighty ash-tree named Yggdrasil, so vast that its branches shaded the whole earth and stretched up into heaven where the Æsir dwelt, while its roots sank far down below the lowest depth. In the branches of the big ash-tree lived a queer family of creatures. First, there was a great eagle, who was wiser than any bird that ever lived—except the two ravens, Thought and Memory, who sat upon Father Odin's shoulders and told him the secrets which they learned in their flight over the wide world. Near the great eagle perched a hawk, and four antlered deer browsed among the buds of Yggdrasil. At the foot of the tree coiled a huge serpent, who was always gnawing hungrily at its roots, with a whole colony of little snakes to keep him company,—so many that they could never be counted.
Either the eagle or the hawk could be Yveltal- A great bird.First, there was a great eagle, who was wiser than any bird that ever lived—except the two ravens, Thought and Memory, who sat upon Father Odin's shoulders and told him the secrets which they learned in their flight over the wide world. Near the great eagle perched a hawk.
The deer, Xerneas.And four antlered deer browsed among the buds of Yggdrasil.
The snake is Zygarde, and all the little snakes, its cells and cores.At the foot of the tree coiled a huge serpent, who was always gnawing hungrily at its roots, with a whole colony of little snakes to keep him company,—so many that they could never be counted.