Answer:
Well, i have gotten the legendary Pokemon (dialga or palkia). I kinda don't remember the way so just go through some caves and you will be there. But remember, there will be some galactic grunts on the way so bring some potion if your Pokemon gets hurt. Or bring one of those spray things that keep wild Pokemon away (i don't remember what its called because i don't play it that much anymore). When you get there, you will have to battle a few galactic grunts. When you defeated them, sooner or later your rival (whatever you named him) will be coming to help you battle two captains.(i think he has a munchlax but i don't know how he got that) After you guys won you will be battling boss Cyrus. After you defeated him there will be something wrong with dialga/palkia.And you will see something that's boring so you might wanna press A or watch it.When you caught it professor rowan will come with lucas/dawn and they will take you away from mt coronet (i think). So if you remember your way try to go back there and get an orb for dialga/palkia (this will help them get stronger). Then you can go to sunnyshore city now! And your next legendary Pokemon to catch is the psychic trio,mesprit,azelf and uxi.