Mega Celestar, the Celestial Pokemon.

The Legendary Pokemon of the Eclipta Region.
Regular Celestar's primary type is Celestial, a special type that was discovered in the Eclipta Region, with most of the pokemon that get it being regional forms (and Minior), while their secondary type can be either Fire, Water or Grass, depending on which evolution stone is used on it.
Mega Celestar is Celestial / End type.
The End type is also a type from the Eclipta Region, primarily given to Shadow Pokemon, replacing their secondary type. It has no resistances and only one weakness, to Celestial.
Celestar's signature move is Supernova, a Celestial Type special version of Head Smash.
Regular color scheme is primarily blue and purple, while shiny color scheme is primarily yellow, red and purple.