Try to use a Water Type Pokemon, it shouldn't be too hard then. If you don't have a Water Type, use an Ice Type or a Ground Type. Ghost and Fighting Types will also be effective.
8th gym leader
you beat the gym leader
A washing machine
in the fortree city
you go to blackthorn city to fight the 8th gym leader
You have to beat the gym leader to gain acess to the Dragon Den. (the 8th gym leader,the on in the town)
Go to Evergrande City to beat the Elite Four
You have to beat the 8th gym and then go back to the museum
The only way to get a gym badge is to challenge the corresponding gym leader and win.
You either go and beat the 8th gym leader Geovanni in Viridian or go to with bill to the island and train plus do him some favours
In the original Pokemon Silver you had to beat the 8th gym leader, Claire, then she allowed you to pass.
you must beat the 8th gym leader and she will grant you passage to dragons den