The reasons why your Rayquaza isn't migrating to Diamond could be the following reasons:
1. Your Diamond game card or your Ruby game pak could be fakes.
2. You haven't unlocked the migration feature in "Diamond" yet.
or
3. Your Rayquaza knows a HM such as Fly or is holding mail.
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No, you have to migrate it from Pokemon Emerald, Ruby or Sapphire. No, you have to migrate it from Pokemon Emerald, Ruby or Sapphire.
Registeel is unobtainable from Pokemon Diamond and Pearl. You have to migrate it from Pokemon Ruby, Sapphire, or Emerald.
Migrate from Emerald, sapphire, ruby, or trade with heartgold and soulsilver
You cannot catch Rayquaza in Pokemon Pearl. You will have to have caught it on Ruby/Sapphire/Emerald and migrated it to Pearl. Then you have to catch it at Pal Park.you cant catch rayquaza in pearl. you can only migrate from ruby,sapphire,or emerald or use cheat with action replay. you have to migrate it from ether Pokemon rudy/sapphire or emerald To get a Rayquaza in Pokemon Pearl you will need to trade with Pokemon HeartGold or SoulSilver. To access Rayquaza in Pokemon HeartGold or SoulSilver you need to show Professor Oak a Kyorge and Groudon. This will give the player a Jade Orb that can be used at the Embedded Tower to access Rayquaza in Pokemon HeartGold and SoulSilver. This Rayquaza can be captured and then traded to Pokemon Pearl.
You'll need to migrate it to the Pal Park from Pokemon Sapphire, Ruby, or Emerald.you can not you must trade or migrate