To defeat or "beat" the 7th gym leader in Pokemon sapphire there twins and they have a solrock and a lunatone to beat them I suggest about level 40-50 water types.
get a level 60-80 exploud that did the trick for me.
get a pokemon, then you train it, get it really strong, and beat th ecrap out of all the 7th leader's pokemon. Its easy.
yes its not easy but its possible so just keep trying!
They are both in mossdeep city. Make sure you have 2 powerful Pokemon that can beat rock and psychic types!
Beat the elite for many times and let your Pokemon hold amulet coin to double the money.
Yes.
latias
u get beldum after you beat the champion u go to his house in Mosdeep city near the seventh pokemon gym it is on his table just take it.
use psychic Pokemon and beat all the trainers to get more light
unova
Get Kyogre..