"Pokemon: FireRed" is an upgraded version of the "Pokemon Red" game that was first published in 1996. This game was published by Nintendo and designed for the Game Boy Advance hand-held gaming system. In the original "Pokemon Red," the Mew character could be obtained only through the Nintendo company, and there was no way to catch the creature. However, you can obtain Mew in "Pokemon: FireRed" with a GBA Action Replay device.
Slide the "Pokemon: FireRed" game into the GBA Action Replay device and attach the device to the bottom of your Game Boy Advance.
Turn on both the GBA Action Replay device and your Game Boy. Choose the "Code Entry" option to open the code entry screen.
Type the following code directly into the code entry screen:
Hit "Enter," and Mew should appear in Box 1, Slot 1 of your Pokemon listings.