in the japanese version you can get the gs ball, and go to kurt, then ilex forest, but only in the japanese version, otherwise, you cant get celebi, mew, you can get in blue/red/yellow w/ the gambler trick, its where you dont battle the youngster w/ the slowpoke (the one not agaisnt the wall) north of nugget bridge, and the gambler west of lavender, the one farther away, go to the little house above, RIGHT in front of the door, dont get in the path of the gambler,
SAVE, be prepared to battle a level 17 slowpoke and have a pokemon that knows fly and have a pokemon ready to catch a level 7 mew, and balls to catch it w/, now go down one step and press start reallllly quick, i got it first time, use Fly, go to curlean, he will see you and have the ! above his head, but you will fly away, then go up nugget bridge to the younster, make him walk to you, DONT step right in front of him or press start, it will freeze the game, battle him, then after you beat him, press start and fly to lavender town, walk west towards the route again, when you go over, your menu should pop up, go down to exit and press exit, then boom, you will run into a level 7 mew, and there you go, that is only red/blue/yellow though, so you would have to trade it over