Use a Master ball. O:] but.. wait you've to clone pokemon and items in Emerald before you catch Rayquaza with a Master ball.
In that case
Go at battle tower in battle fronteer
1. Equip the Pokemon with the item you want to clone;
2. Put that Pokemon in a box, doesn't matter which one;
3. Save;
4. Withdraw the Pokemon from the box;
5. Talk to the lady on the far right and agree to do the challenge;
6. Say Yes to the need to save the game;
Now, you have to wait a second before it gives the saving prompt.
7. Do NOT Save, instead, reset (soft and hard both work) the game;
8. When you turn on the game, you'll have the Pokemon in your team and in the box (with the item).
You can clone up to five Pokemon per try this way.
Have fun!
