Things You'll Need
Instructions
Use the Action Replay software CD to download and install "Action Replay Code Manager" onto your computer. Go to your start menu and select the new application to run "Action Replay Code Manager." Insert the Action Replay cartridge into your Nintendo DS. Use the supplied USB to MINI USB lead to connect the cartridge with the software.
Place "Pokemon Platinum" into the "Pass Through" port of the Action Replay cartridge. Switch your Nintendo DS on. Wait for Action Replay to recognize "Pokemon Platinum." Choose the "Code Select" button.
Select the "Codejunkies.com" tab under the "Subscriptions" window of "Action Replay Code Manager." Click on the "[+]" sign and choose the "UK" code list. Look for "Pokemon Platinum" in the code list and click on the name to highlight it.
Look for the "Wild Pokemon Are Shiny" cheat and the "Rayquaza" cheat. Drag and drop each code onto the "Nintendo DS" window. "Action Replay Code Manager" will download the two codes to the code list on your Action Replay cartridge.
Choose the "Wild Pokemon Are Shiny" cheat and the "Rayquaza" cheat from the "Code Select" screen of your Action Replay DS. Return to start menu of Action Replay DS and press "Start" to play "Pokemon Platinum" with the two cheats enabled.
Load your "Pokemon Platinum" save file. Walk around in any cave or long grass on any route until you encounter a Shiny Rayquaza. Weaken it with Ice-type moves and catch it with an Ultra Ball.