Wild Pokemon Modifier Code
Enter this code into your Action Replay DSi:
94000130 FCFF0000
62111880 00000000
B2111880 00000000
00000D14 01ED0001
D2000000 00000000
94000130 FDFF0000
62111880 00000000
B2111880 00000000
DA000000 00000D16
C0000000 00000027
D7000000 00025A68
D2000000 00000000
Using the Wild Pokemon Modifier code to get Mew
The Wild Pokemon Modifier code forces the game to have the Wild Pokemon of your choice attack you. When it does, you can battle and capture it as you would normally would.
With the code entered into your Action Replay DSi, start your game, hold down the "L" and the "R" buttons on your Nintendo DS, then check your inventory. You will now have 999 Master Balls. Discard the balls until their number is the same as the Pokedex number of the Pokemon you wish to encounter. When you have the appropriate number of balls in your inventory, exit your inventory and hold down the "L" button.
Mew
Depending on which installment of the game you're playing, Mew's Pokedex number is 151, 255, or 306. You find out which by checking your Pokedex. Discard the Master Balls until you have as many as Mew's number, then weaken it enough in the following battle to capture it.
Celebi
Like Mew, Celebi's number changes with the installment you're playing. It is either 256 or 386. Also like Mew, Celebi is very, very powerful, so do not attempt to capture it using this code until you have a high level Pokemon capable of standing its ground against Celebi.