Celennial- A massive dragon of the stars that observes the Pokemon world from space. It is rumored to be the source of sunlight and the twinkling stars in the night sky.
HP- 150, Attack- 100, Defense- 150, Special Attack- 200, Special Defense- 150, Speed- 100
It wouldn't be capturable. I envision it as a final boss fight where you and all your friends go and fight it together, culminating in a 5 v 1 battle. Pokemon Shining Star would be the name of such a game.
Attacks: Solar Flare, Orbital Derailment, Asteroid Strike, and its signature move Supernova
It would be a legendary that would be truly legendary, meaning it is super powerful but can't be caught by trainers.