As Mega Rayquaza is confirmed for Pokemon Omega Ruby and Alpha Sapphire, more information on its Evolution has been revealed, including why it does not go into Primal Reversion like Groudon and Kyogre.

Reportedly, Mega Rayquaza holds a new Ability called Delta Stream, which creates a new weather effect that projects Flying-type Pokemon. In the trailer featuring Mega Rayquaza also shows a new move called Dragon Ascent, which is said to be the most powerful Flying-type move of all.

According to Serebii, the reason why Rayquaza has a Mega Evolution and does not go into Primal Reversion will be explained in Pokemon Omega Ruby and Alpha Sapphire. In addition, it will also Mega Evolve through a new method of Mega Evolution.

And while fans theorize over why Rayquaza has a Mega Evolution and not a Primal Reversion, the lore behind this Legendary Pokemon has been posted on the official Pokemon Omega Ruby and Alpha Sapphire website, which also mentioned Primal Kyogre and Primal Groudon.

"It was a primal age, early in the world's history..." said the description. "The natural world was overflowing with energy. That energy granted Groudon and Kyogre an overwhelming power. Seeking ever more of that energy for themselves, the two clashed again and again, and their battles cast the people and Pokémon of Hoenn into great danger. Brimming with the overwhelming power granted by the energy of nature, this transformation was named by later people 'Primal Reversion.' And the people called their tormentors Primal Groudon and Primal Kyogre."

"One Pokémon looked down upon this battle from the sky above. The Pokémon that dances in the heavens: Rayquaza. Rayquaza is venerated by the people of Hoenn as their protector and savior. When Primal Groudon and Primal Kyogre had battled for 20 dawns and 20 nights, the world began to lose its natural balance and tilt toward destruction. The people, unable to endure any more, cried out to their mighty savior Rayquaza before a great stone that shone with rainbow brilliance. And a change came upon Rayquaza, weaving in the sky above Primal Groudon and Primal Kyogre. Suffused in brilliant light, its body began to transform visibly. And then..."