I've heard that the only way to get Manaphy or Phione on Diamond/Pearl is to transfer them from Pokemon Ranger, so i just have two questions:
1 - Which pokemon ranger game is it?
2 - Can you transfer any/all pokemon from ranger?
The one you appear to be referring to is Shadows of Almia. There were only 3 Pokemon you could transfer to D/P/Plt: Darkrai, Manaphy, and Riolu(With Aura-sphere). I use the Past tense because these were event Pokemon on the ranger net and are no longer available. So there is no way you can get these Pokemon through Pokemon ranger. Though the new Pokemon Ranger game (Guardian signs) may have some more events left but I am not sure. I hope I helped :)
first you transferr it from shadows of almia or the first one but i think you need a wireless internet connection. and second no you can only trade manaphy to the games that i specified.
sources: research on the pokemon wiki
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