Things You'll Need
Instructions
Insert the "Pokemon Emerald" game cartridge into the bottom slot of the Nintendo DS, and "Pokemon Platinum" into the top slot.
Launch "Pokemon Platinum." Select "Migrate from Emerald" on the main menu, and "Yes" when prompted.
Select Groudon, Kyogre and Rayquaza and any three other Pokemon. You must transfer six Pokemon at a time.
Tap "Yes" twice to transfer the Pokemon. "Pokemon Platinum" restarts automatically once the transfer is complete.
Load your saved "Pokemon Platinum" game.
Travel to the Pal Park, located on Route 221. Speak to the man behind the desk and select "Enter" to enter the Pal Park.
Travel to the region in the Pal Park associated with your Pokemon. Rayquaza is found in any patch of tall grass in a grassy area, Groudon is found in any patch of tall grass in the mountainous area, and Kyogre is found in the oceanic area.
Walk in the tall grass in the mountainous or grassy area, or surf in the ocean, until your Pokemon appears. When the Pokemon appears, your character automatically throws a Park Ball at it, which instantly catches the Pokemon.
Catch all six transferred Pokemon. There is no time limit, so you can take your time. Once the last Pokemon is captured, you regain ownership over the transferred Pokemon and can use them as you wish.