I just used these action replay codes warped to birth island and (turned the switch off on the action replay after i warped there)(you warp whenever you go in out a building) and caught deoxys....
same with mew....
i found these codes posted
they work
again you have to get to the places and turn the codes off or you could not get to the pokemon or leave...
(M)(ALWAYS MUST BE ON)
D8BAE4D9 4864DCE5
A86CDBA5 19BA49B3
(DMA Disable)(MUST BE ON ALONG WITH THE MASTER CODE)
06122196 8FE98260
65DA389A 09D8882C
Warp codes
Southern Island: 7703F025 00394020
Faraway Island (Mew): 82CBD483 7B9D8E0B
Birth Island (Deoxys): E5AC0043 E1C4C8F0
Navel Rock (Lugia and Ho-oh): B5B9E5C0 B11CE872