Things You'll Need
Instructions
Turn on "Pokemon Emerald" and enter the Gameshark code "19C67C656689
94318A10E753." This will warp you to the "Far Away Island."
Walk through the grass until you see Mew. Attempt to fight her. She may run away at first, but this is normal. Keep persuing her and eventually you will be able to battle. Once Mew's health is low, throw a Pokeball to capture her.
Enter the Gameshark code "19C67C656689 12B9BF13D649" to warp back to Mauville City. Enter the Pokemon Center and go up the stairs on the left side of the building.
Turn on your second Game Boy Advance and begin to play "Pokemon Fire Red." Navigate to a Pokemon Center and go up the stairs on the left.
Plug the link cable into both Game Boy Advances. Talk to the character standing behind the desk. She will ask you if you would like to trade. Select "Yes" on both Game Boy Advances.
Enter the "Union Room" and talk to the trainer. This will start the trading process. Select Mew from "Pokemon Emerald" and trade it to "Pokemon Fire Red."
Exit the trading room once the Pokemon has been swapped. Save your game. You will now have Mew.