Mauville city.
1950s
you go to victory road
u have 2 get the 17 badge after go to cinabar island and talk 2 the only man outside of the Pokemon center hell look 2 see how many badges u have if u have all but the last badge hell go back 2 the gym in and u can battle him be careful hes tough(:
Type 'battle gallery' in the search place. go 2 the page. click on capt reynolds. voila get the badge
go to the north rustboro (city where you get the rock badge) where the woman is, go to the beach and surf between the light brown rocks. You find a forest with 2 trainers and some weird looking berries, go in.near the karate guy you find some stairs and a pokeball, in that pokeball is tm1
go to the little house in celestic town.make sure your all your badges have 4 sparkles on it.then stand in front of the little house and follow this gym badge pattern: badge 2; badge six; badge 5; badge 7; badge 3;............................................. man i forgot! just go to youtube and type this:pokemon diamond-how to capture celebi and look for how to capture celebi(no codes!) WARNING!THE VIDEO CAN GO A LITTLE FAST DURING THE BADGE PART SO HERE'S A TIP: pause each time the video hits a badge.
Go to Mossdeep city and beat the gym.
u go 2 farawayland
go 2 mt.cornet top {beware u need 2 beat Cyrus there}
go to Eterna city and defeat the gym leader(she has grass type pokemon).
u must go 2 cianwood city get the medacin and bring it to the light house
get the hm waterfall (forgot were u get it) and go 2 the Pokemon league climb the waterfall and go in 2 victory road 2 the other side! Hope i helped! : )