Things You'll Need
Instructions
Connect your Action Replay device to your computer through its USB cord.
Open the Action Replay Code Manager software that comes with the device.
Right-click on the "My Codelists" panel of the screen. A small list of options will appear.
Click on "Create new cheat." A new window will appear.
Enter Mew's Action Replay code into the window:
39E924C4 4136A9DD
B751BDF4 95CEF4CC
Click "OK" to close the window.
Click "Save" from the "File" menu on the top toolbar. The changes will be saved to your Action Replay device.
Load a saved game or create a new game in "Pokemon Sapphire."
Enter any area in which you can battle Wild Pokemon. These areas include tall grass locations and caves. The only Wild Pokemon you will be able to encounter is Mew, so any time you enter into a battle, it will be against Mew.
Capture Mew by weakening his health and catching him with a Poke Ball. The Pokemon will be level 30 for the battle, so you will need to fight him with a Pokemon around the same level. As a Psychic-type Pokemon, Mew is weak against Fighting-type Pokemon. Once you catch him, the Pokemon will be stored in your inventory for you to use at a later time.