there are no 20 gym leaders
go right from the seventh gym leader
Go down to oreburgh mine and talk to the gym leader he will run off now go to oreburgh city and go into gym that gym leader will challenge you.
which gym leader?
go catch Giratina and then go to the Sunshore City gym and fight the gym leader
The seventh gym leader
go to the ligthouse then talk to the blonde guy he is the gym leader then go to the ggym
Go to Mawille(eletric gym town) and there will be a gym leader... there is no gym leader
You go to Fortree City to take on on the flying type gym leader!
go to hearthome city and fight the gym leader there
You go on to defeat the eight gym leader.
Go to the lighthouse and the Gym leader should be there.
You have to go to Veilstone City and go to the gym. Then you battle gym trainers and go past them. You will get to Maylene, the third gym leader. You can battle her. Unless you're talking about the Hearthome Gym. Fantina is the leader of that gym. If that's what you meant, you need to fight the Veilstone Gym and the Pastoria Gym first.