You can't anymore, but there were a few special events, so if you get wi-fi, you could always ask to trade for one.
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You can't change Shaymin into Sky Form in Pokemon Diamond (that includes pearl). You can only change Shaymin into Sky Form in Pokemon Platinum (that includes Heart Gold and Soul Silver). You can get the Gracidea to change Shaymin into Sky Form.
u cant.
Shaymin, and 463 is Arceus
shaymin
You can't get shaymin in heart gold you have to trade it from Pokemon pearl,diamond or platinum.