The video below shows Ramanas Park in detail.
Firstly, the video shows the player using an item called a Slate to trigger an encounter. So, it seems that players must find Slates in order to encounter and catch legendary Pokémon in Ramanas Park. Subsequently, I wonder how players find Slates. Are they randomly hidden or is there perhaps symbolic intent to their placement? For example, it would be a nice touch if the Slate used to encounter Rayquaza was in a ruined tower-like Sky Pillar.
It appears that Ramanas Park is located where Pal Park was in Pokémon Diamond, Pearl, and Platinum. Pal Park allowed players to migrate Pokémon from Generation III games to Generation IV games. So, it seems like the migrate feature isn’t returning.
How will players transfer Pokémon from the previous generation to Brilliant Diamond and Shining Pearl? Based on the confirmation that these remakes will be integrated into Pokémon Home in 2022, the likely answer is that players will simply transfer Pokémon from Pokémon Home directly into their Pokémon BDSP PC boxes.
Pokémon Brilliant Diamond and Shining Pearl are just over a week away. Fans can play BDSP on November 19th, 2021.