We now have official information about the new type of Pokemon evolution in the upcoming Pokemon Alpha Sapphire and Omega Ruby games. It’s called Primal Reversion and it makes the two legendary Pokemon from the games’ covers, Groudon and Kyogre, even larger and more fearsome.

Developer Game Freak revealed the new forms on its website today and provided some information about Primal Groudon and Primal Kyogre. Primal Reversion involves the two Pokemon seizing some of the natural energy around them and using it to transform into the forms they had during ancient times.

According to the developer: “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. 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.”

With this announcement, Game Freak also confirmed that the Pokemon on the covers are, indeed, the Primal forms of the two legendaries.

Through Primal Reversion, Groudon and Kyogre gain even more power and grow significantly larger. Groudon’s Attack stat increases, and it becomes a Fire Type pokemon. Its special Ability changes. Kyogre’s Special Attack stat increases, and its special Ability changes, too. However, Game Freak is keeping the details of the Ability improvements a secret at this time.

Nintendo announced Pokémon Omega Ruby and Alpha Sapphire last month. They are remakes of Ruby and Sapphire, but they are described as “fresh takes” on the originals. They are due out on November 21 for the 3DS.