What is the process of turning Groudon into Primal Groudon in Pokemon Omega Ruby and Alpha Sapphire?

Answer 1

well when u get far enough in the game u obtain this primal stone for groudon, give it to him as a held item and then go into battle, he will primal evolve right when the battle begins and can happen many times, not just once a battle

Answer 2

The process of primal reverting Groudon and Kyogre in Pokémon Omega Ruby and Pokémon Alpha Sapphire is that you will need the color-coded orb for the Legendary Pokémon that you want to revert so the Red Orb will be for Groudon and the Blue Orb will be for Kyogre the next objective is to attach the orbs to the related Pokémon and then as soon as they enter battle they will automatically primal revert and even though they do so automatically they do not count against the "One Mega Evolution per battle" limit so you could have Primal Groudon, Primal Kyogre and a Mega Evolution all in the same battle.