How do you unlock the Delta Episode in ORAS?

Question

I've just got Pokemon Omega Ruby and I've heard you get Rayquaza in one of the 'delta episodes'. What are these and how do you open them?

Answer 1

The Delta Episode (Japanese: エピソード　デルタ Episode Delta) is a mission following the player's first completion of the Hoenn League in Pokémon Omega Ruby and Alpha Sapphire.

You unlock the Delta Episode after beating the Elite Four and Champion for the first time. After doing so, the Delta Episode starts. Also, I would like to note that the Delta Episode is one thing, there are not multiple Delta Episodes.

Source (Contains spoilers for the Delta Episode. You have been warned.)

Answer 2

The Delta Episode is something that is accessible after beating the Elite Four and the Champion. The Delta Episode is a part of the game that continues the storyline of the game after you think your adventure is finished. It gives you access to more legendary Pokemon such as Deoxys and Rayquaza. This can also be used to have another attempt at catching Primal Kyogre or Primal Groudon if you were not able to catch them before. This can also work with any other legendary as well.

I hope this helped!