most likely on battle island
you talk to this little girl in sandgem town and she tells you once a day where to find a pokemon. hope this helped :)
on platinum, you see Manaphy in Mr.backlots Pokemon mansion
You can't see him in platinum. You have to transfer it from Pokemon Ranger
Nope, you can't see Ash in Pokémon Platinum.
You can't see Manaphy in Pokemon Platinum, but I might trade you one. My email is likefruit89@yahoo.com.
Route 201
battle everyone
Throw a pokeball at it when you see it.
You can't catch it in Pokemon Platinum but you can get it in Pokemon Pearl in Eterna Forest at night or in the Lost Tower.
battle trainers or catch the Pokemon
you cant!
you have to migrate