you must send him over from a pearl or diamond or cheat (Action replay or hacking)
The only way to get Shaymin in Platinum without cheating or an event is through trading it with a friend.
Go to the Shaymin event. :)
Shaymin is only avalible through an event, which is now over. :(
The only way to get Oak's Letter as a Mystery Gift was to wait for an event, go to that event, and then download it as a mystery gift. However, the event to get Shaymin in America for Diamond and Pearl has already passed, so it is impossible to get it as a mystery gift now. There has already been a Pokemon Event for Shaymin (what you need Oak's Letter for) for Pokemon Platinum, so that has passed, too.
One for every event Pokemon like Shaymin, Darkrai and the special Regigigas.
Event
You won't get it. you can only get the Gracidea flower in Pokemon Platinum. If you got the shaymin from diamond and put it in platinum it wouldn't work, you have to get a event shaymin from mystery gift or go to toys'rus at certain times. You can also get it in HG/SS in the flower shop in goldenrod city. that also involves the event shaymin.
you must use mystery gift -MEjkl
Yes, Shaymin is an event Pokemon.In order to retrieve it you must have Mystery Gift and Wi-fi.You download Oak's Letter on mystery gift from September 28, 2009 to November 1st, 2009. After this is over you will no longer able to get Shaymin legally.
yes but you have to have oaks letter and that is an event item which you can no longer get
because it is not an event shaymin
yes or get the oak's letter from the event which past