Encountering a Shiny Rayquaza Pokémon is completely random. However, players can reset the game until they encounter the Shiny version. First, save the game before interacting with Rayquaza. After saving, approach Rayquaza, and allow the battle animation to begin. If Rayquaza is not Shiny when it appears within the battle animation, reset the game, and try again. Continue this process until Shiny Rayquaza appears.