"Primal Reversion" is a mechanic similar to Mega Evolution, but specific to Groudon and Kyogre in Pokémon Omega Ruby and Alpha Sapphire. While the mechanics are similar, they are not the same as Mega Evolutions, requiring different circumstances and taking a different name.

Primal Groudon has a duller red coloration than the normal form with wide, bright orange/yellow striations on the body, with bright red eyes. The teeth and spikes along the body have turned from white to the same grey as the underside, the fins on the end of the tail are splayed, the mouth shines the same bright orange/yellow as the marks in the body, and the upper arm bears the token "omega" symbol for Omega Ruby.

Primal Kyogre has a darker blue shade than the normal form with bright blue and yellow striations in the body, including light patches on the fins. The eye sclera is now bright yellow with bright orange irises, the hind "streamer" fins are much longer with a gradient yellow-blue stripe down the center, and the both the face and upper sides of the front fins bear the token "alpha" symbol for Alpha Sapphire.

Note: This is not the same mechanic as Primal Dialga in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness, or Pokémon Mystery Dungeon: Explorers of Sky, despite the similar names. Primal Dialga should not receive the primal reversion tag. Also, because these are not Mega Evolutions, they should not receive the mega evolution tag.

Normal Groudon: post #494650
Primal Groudon: post #494654
Normal Kyogre: post #494653
Primal Kyogre: post #494655