You have all but one Pokemon in Pokemon Diamond and Pearl. This Pokemon is Manaphy, which can only be obtained by owning a copy of Pokemon Ranger. If you press the right buttons and use a code, you too can have a Manaphy egg.
Steps
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Step 1. Insert the Pokémon Ranger cartridge into your DS system and turn it on
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Step 2. Complete the Continuous Missions in Pokemon Ranger
Afterward, you should notice a new entry on the title screen; Ranger network.
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Step 3. Press and hold the R, X and left buttons
Enter Password will appear under "Select mission". Press that voice.
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Step 4. On the Enter Password screen, type Mg35-Cpb8-4FW8 if you have a European cartridge
- P8M2-9D6F-43H7 if you have an American cartridge.
- C58f-t3WT-Vn79 if you have a Spanish or Portuguese cartridge.
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Step 5. On the Select Mission screen, choose "Save the Precious Egg
".
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Step 6. After completing the mission, Check Egg will replace Enter Password in the Ranger Network menu
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Step 7. When ready, enter Pokemon Diamond or Pearl in a second DS
Turn it on, and go to the Main Menu (Continue, New Game, etc.).
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Step 8. In Pokemon Ranger, press "Check the Egg", and press the screen
Then, press 'Send Message', and bring the 2 DS closer together.
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Step 9. In Pokemon Diamond or Pearl, a new screen will appear
From here on, follow the instructions provided.
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Step 10. Congratulations, you have a Manaphy egg in your version of Pokemon
- To make it hatch, go to any PokeMart in the Sinnoh region and talk to the man in green. He will give you the egg (as long as you have a free spot on the team).
- Walk approximately 2740 steps. The egg should hatch.