just level it to 59 or whatever
nothing stupid, just find groudon after you beat the 7th gym leader and go to the place where you beat the 8th gym leader .then you will find Steven and he will lead you to a cave and keep on walking until you find groudon.
you have to beat groudon then surf to the middle of the city with the last gym in it
8th gym leader
The eighth gym leader is in the underwater city(forget the name) but it is where you fight groudon. after you beat him the gym should be open.
you beat the gym leader
go and beat the 8th gym
You must go to the hidden cavern that is located in Mossdeep. Once inside the cavern beat all the Pokémon inside and also beat Team Magma leader. Then go to the cave of origin in Sootopolis City and catch Groudon. Once you catch Groudon the gym door will unlock.
Beat the 8th Gym leader.
Go Beat the elite four. And catch the legendaries like Kyogre and groudon. =]. -egyoshi
The only way to get a gym badge is to challenge the corresponding gym leader and win.
you go to blackthorn city to fight the 8th gym leader
the potion is in the pharmacy in cianwood city