Evolving Mega Altaria costs 300 Mega Energy the first time, and 60 Mega Energy every other time.
Standard game images
There is a very low chance that you can get a shiny Mega Altaria, which has the following appearance:
About
"Altaria dances and wheels through the sky among billowing, cotton-like clouds. By singing melodies in its crystal-clear voice, this Pokémon makes its listeners experience dreamy wonderment."
