Aura Trio

The Yggdrasil Trio is a trio of Legendary Pokémon that originates in the Kalos region and comprises Zygarde, Xerneas, Yveltal. Yggdrasil is a huge tree in Norse cosmology. It is said to be protected by three guardians.A bird protects The upper part of tree.A Deer protects the soil of tree.A snake protects the underground of tree. Same is true for Xerneas, Yveltal and Zygarde.

Trivia

 * Xerneas is the only type to be part of legendary trio.