Instructions
Attend a Nintendo-sponsored event to get the key item, "Oak's Letter," for "Pokemon Platinum." Check on upcoming events through the official Pokemon website or the Serebii website (see Resources).
Travel to Route 224 in "Pokemon Platinum." Route 224 is located in the northeastern part of the Sinnoh Region. It is to the north of the Pokemon League, to the south of Seabreak Path and to the southeast of the Fight, Resort and Battle Areas. Now that you have Oak's Letter, Route 224 will be longer than it once was. Travel the full length of the path.
Approach the field of flowers at the end of Route 224. Shaymin will appear standing among the flowers. Approach Shaymin to initiate a battle with it. When battling it, avoid using Water, Grass, Electric or Ground-type Pokemon against it; for the best results, use Fire, Poison, Flying, Bug or Ice-type Pokemon. Weaken Shaymin through attacks and use a Poke Ball to capture it.
Enlist a friend who has a second Nintendo DS system. Insert the "Pokemon HeartGold" game into this Nintendo DS. Both players should travel to the Oreburgh City Wi-Fi Club to earn the Pal Pad.
Swap "Friend Codes" with your friend. Both players should open the "Main Menu" and select "Bag." Open "Key Items" and select "Pal Pad." Select "Code" beneath your character's name to find your friend code.
Open the "Main Menu" and select "Bag." Open "Key Items," select "Pal Pad" and select "Register Friend Code." Enter information such as your friend's name and friend code. Select "OK" after you enter the information. Select "Yes" to finish registering your friend's code.
Travel to any Pokemon Center and go to the bottom floor. Both players should speak to the Wi-Fi Club representative. Select "Yes" four times to save your games and enter the trade screen.
Select your friend's name in the trade menu, select "Invite" and then select "Trade." Select the Shaymin and select "OK" to trade it to the "HeartGold" game. Select "OK" again to accept the trade. Both players should save their games.
Play "Pokemon Heart Gold." Shaymin should be stored in your Pokemon party or in the PC.