Answer:
if you mean the code to obtain him, then here is the code. first you need to have an action replay to enter the code in, and then you need to click on the new code button, and then call the code's name whatever you'd like it to be. then here comes the code. make sure you type it in right.
94000130 FDFF0000
B21C4D28 00000000
B0000004 00000000
94000130 FEFF0000
00000890 01ED0001
D0000000 00000000
DA000000 00000892
DC000000 00024620
C0000000 0000000B
D7000000 00000000
DC000000 00000006
D2000000 00000000
Then you turn on your game and i recommend that you go somewhere where there are strong Pokemon, because whatever level Pokemon are there, is what level your mew will be. then press L+R to activate the code. now, look in your bag and you shouldhave 493 master balls. if you are a Pokemon freak, you know that number is arceus. now if you want to know that your code if working, then toss out 1 pokeball. That will leave you with 492 balls. that number is shaymin. now, walk in grass holing L ONLY, and then shaymin will appear. if it doesn't your not holding down L or you are holding down L+R. if it does, your code is working! if you want to, you can catch him, or you could have tried it with arceus. Now that you know that the code is working, you go into your bag again, and subtract 341 pokeballs {340 of you used one to capture shaymin} and now you will have 151 mew number. now, hold down L and then you will find mew! I hope you catch him! {P.S. you can catch him multiple times!}