The starter Pokemon in Pokemon Diamond are Piplup, Chimchar, and Turtwig.
piplup
you can get it as your starter Pokemon
You cant. You have to trade pokemon.
Turtwig in Pokemon Pearl and Diamond.
you get piplup as a starter in Pokemon diamond/pearl/platinum
I'm pretty sure that the only way to get another starter Pokemon in Pokemon diamond is to go to the Global Trade Station (GTS) and trade with someone.
evolve the water starter
Turtwig Chimchar Piplup
You Get It When You Visit Professor Rowan After You Get Your Starter Pokemon!
You have to get Piplup for the starter Pokemon and level him up or trade for it.
All I can say is luck
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