You can use the GTS in Pokemon Platinum after you get the first gym badge from the Oreburgh City gym.
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If you have Deoxys in the Pokedex, you can find it in the GTS if anyone's trading one.
You have to get a badge and have Wi-fi connection. Go to the left when you're at the Pokecenter. For more information contact me at likefruit89@yahoo.com. what is gts?
You have to go into the GTS once
You can't the only possible way to get rayquaza in platinum is to transfer it from emerald, get it at GTS (you must have seen a rayquaza to get it at GTS) or use AR (Action Replay). hope this helped.
Try the GTS trick.