Here's some official information about the Primal Reversion you'll see in Pokemon Omega Ruby and Alpha Sapphire.

The official Pokemon website has new information about the beings on the covers of the games, Primal Groudon and Primal Kyogre. The post recounts the Hoenn legend of the weather legendaries, Groudon and Kyogre. But apparently there was more to the legend than originally thought. A new passage continues the tale:

It was a primal age, early in the world’s history. 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 to them by nature’s energy, their transformation was named "Primal Reversion" by later people. And the people called their tormentors Primal Groudon and Primal Kyogre...

Through a process called Primal Reversion, Groudon and Kyogre assume their Primal forms and receive new bonuses. For example, Primal Groudon gains Fire type, has a high attack and defense and can control the weather with its Ability.

Primal Kyogre, on the other hand, gets a boost in Sp. Atk and its body composition almost becomes that of seawater's. It has a hidden Ability which has yet to be announced, but we're hoping it's a game-changer.

Look out for these two Primal legendaries when Pokemon Omega Ruby and Alpha Sapphire are released on Nov. 21 for the Nintendo 3DS.