How to reach Ramanas Park and catch Legendary Pokémon there.
What is Ramanas Park?
Ramanas Park was added to Pokémon Brilliant Diamond and Shining Pearl in version 1.1.0. It is a place where you can catch Legendary Pokemon after you obtain the National Pokédex and defeat the Elite Four and Champion.
How to Reach Ramanas Park
Make sure you are playing version 1.1.0 or higher and you have the National Pokédex and have entered the Hall of Fame (see above). To reach Ramanas Park, first use the Town Map to fly to Sandgem Town, then go south from there to Route 219, and check on the water there. Make your way south to Route 220, then go south onto the island just south of the two swimmers. Go east and pick up the Ether, then go east into the water. Go east from there and you will battle Swimmer Erik (and possibly Swimmer Claire at the same time in a Double Battle). Keep going east to Route 221, and go east to land on the grass. Go east from there and battle Collector Ivan, then you can go east and north into Ramanas Park, where Professor Oak will greet you. From now on, you can fly to Ramanas Park using the Town Map.
How to Catch Legendaries in Ramanas Park
Before you can catch Legendaries in Ramanas Park, you need to find Mysterious Shards in the Grand Underground. Mysterious Shards start appearing in the digging mini-game in the Grand Underground after you defeat the Elite Four and Champion.
When you have at least 3 Mysterious Shards S, or 1 Mysterious Shard L, you can go to the counter in the Ramanas Park building and purchase a Slate. Then go through the rear exit of the building and enter one of the 8 caves. If you're in the cave that matches the name of the slate that you purchased, you can check the pedestal to put the slate in. You will be teleported to Pure Space, where you can talk to a Legendary Pokémon to start a battle with it and try to catch it.
After you catch a Legendary, go back into the Ramanas Park building and you will receive a statue of that Legendary, which you can put in your Secret Base in the Grand Underground to increase the encounter chance of that type of pokémon.
Ramanas Park Map
Oceanic Stratospheric Genome Squall/Rainbow Soul Johto/Kanto Discovery Tectonic EXIT
Legendaries you Can Catch
|Raikou/Entei/Suicune (Brilliant Diamond) or Articuno/Zapdos/Moltres (Shining Pearl)
|Johto Slate (Brilliant Diamond) or Kanto Slate (Shining Pearl) - Available after you catch Regirock, Regice, and Registeel
|Soul Slate - Available after you catch Regirock, Regice, and Registeel
|Ho-oh (Brilliant Diamond) or Lugia (Shining Pearl)
|Rainbow Slate (Brilliant Diamond) - Available after you catch Raikou, Entei, and Suicune, or Squall Slate (Shining Pearl) - Available after you catch Articuno, Zapdos, and Moltres
|Oceanic Slate - Available after you catch Raikou, Entei, and Suicune or Articuno, Zapdos, and Moltres
|Tectonic Slate - Available after you catch Raikou, Entei, and Suicune or Articuno, Zapdos, and Moltres
|Stratospheric Slate - Available after you catch Raikou, Entei, and Suicune or Articuno, Zapdos, and Moltres
|Genome Slate - Available after you catch Raikou, Entei, and Suicune or Articuno, Zapdos, and Moltres
Origin Forme Giratina
After you have caught Regirock, Regice, and Registeel, and you have also caught Giratina in Turnback Cave, you can purchase a Distortion Slate and use it in the Distortion Room to battle an Origin Forme Giratina. You can't catch it, but if you defeat it, you get a Griseous Orb.