Where is pusle in in Pokemon Diamond?

Answer 1

After obtaining the National Pokedex, when you talk to the Pokemon Mansion owner, he will often say stuff like: "I have some wonderful Plusle in my lovely garden." He'll not necessarily say Plusle. He could say Bonsly, Eevee, or some others. But if he does say Plusle, go in to the garden and walk around in the grass. Eventually you'll find Plusle. Another way to get one is to, should you have a copy of Pokemon Ruby, Sapphire, or Emerald, catch one in any of those, and migrate it to Pal Park.