u cant get it , it was a mystery gift from a couple months ago
going to the Pokemon league on a sandbar
You find or get it at Route 210.
you can not get a master ball in Pokemon platinum only the one professor Rowan gives you
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It is really hard to get one. On Pokemon Platinum you need to find PIchu/Pikachu and catch it or use thief and if your lucky enough it will be holding a light ball. I
it was through a Nintendo distribution event and it has already passed...
Defeat Cyrus at the Veilstone Galactic Building.
You can find TM53 energy ball on the battle tower and on route 226.
You get it when you beat the Galaxy Leader in the Base in Veilstone City. He brings it to you!
After you beat Cyrus at the Galactic HQ, he will give you one Master Ball.
buy the Pokemon platinum book
you can get it by getting a pichichu in pearl trade it to heartgold