...ummm...it might be a long time but you have to get to a pokemon event after getting mystery gift...you need to have an Aurora Ticket...you can sail on a ferry to Birth Island afterwards...a rock will be there...you examine it and it moves...follow it in the least number of steps you can possibly take...move it until it cracks into a Deoxys... lv.30 and it's in speed form in Emerald, Defense for LG, and Attack for FR. as for Mew...it's basically the same process, but it's NOT on Birth Island. No, no, it's on Faraway Island, and you need the Old Sea Map. Mew, when you're there, will play hide and seek with you... keep on "winning" to battle it at lv.30. And as a little bonus, I can tell you about Navel Rock. Antoher event thing, in which you need the Mystic Ticket. A cave there will have two paths, take the one that goes up to meet Ho-oh, the one that goes down to meet Lugia. And since I'm such a sweet guy, use itemfinder on the exact spot where Ho-oh was to get a Sacred Ash (revives all pokemon to full health). and what level they are?... I don't know. Happy hunting! (also, you can't do any of this in S/R...and you can't do Mew in S/R/FR/LF either. Just a little tip...hehehe...
Celebi is the best. Latias is right behind. no opinions wanted. leader of S.H.O.K. join my club today! Please?