Get 8 badges
Ghost, Fire, Ground, Psychic, and Ice
route 2 in the island you open after getting past the Pokemon league
u can travel to kanto from olivine,beat all the gyms there and go to the battle frontier which is right past olivine
In Pokemon platinum you must find all the Pokemon in your game to be aloud past so it should be the same in your game
must obtain the required number of league badges
skill
You have to beat the league.
learn whirlpool
Go to sunyshore city, then go up in the water (make sure you got surf and waterfall) to swim and to go up the waterfall to The Pokemon League then you will reach a Pokemon league cave past it and then go to the Pokemon league heal your Pokemon and fight
Well on gold um
beat the Pokemon luegue then go to the Pokemon centre
You can use any Pokemon. As far as I know you don't have to use certain Pokemon to challange them.