94000130 FCFF0000
To use this code, you will need to have an Action Replay or similar cheating device. Once you have the code, follow these steps:
1. Start Pokémon Diamond and load your save file.
2. Open the Action Replay menu and select "Codes".
3. Enter the AR code into the code box and select "Add Code".
4. Save the code to your Action Replay device.
5. Go to Floaroma Town and talk to the man in the flower shop. He will give you a Flower Pot.
6. Plant the Flower Pot in your garden and water it every day.
7. After seven days, Shaymin will appear in the Flower Pot.
Note: This code will only work if you have a Japanese copy of Pokémon Diamond. If you have a North American or European copy of the game, you will need to use a different code.