Help identify this Pokémon

I’ve searched blue Pokémon lists and quadruped lists but can’t figure out what this is (and how to catch it ;-)

It is Shiny Xerneas in its neutral form, I guess :thinking:.

In battles it changes its color.

All Xerneas, when not battling looks blue, in battle it looks as we all know.

image

Aha. Thanks. Did not realize the color changed !