Hoopa have been announced to have a true form and that is only available in Omega Ruby and Alpha Sapphire.
This new form of Hoopa turns him, a Psychic/Ghost type into a Psychic/Dark type. It’s new height is 20x its original and its weight is 54x its original. It’s ability is unchanged and will be one of the main protagonist in Pokemon: Hoopa & the Clash Of Ages movie.
Hoopa Unbound is the true form of Hoopa, which has had its power sealed away. The rings it carries have the power to bend dimensions and are said to allow it to seize anything in the world.