Your best bet is by having a psychic or flying Pokemon, but flying is recommended. You will get Fly after defeating this gym, so you should use a flying Pokemon. You can just have it know powerful flying moves, and the fighting gym will be easy.
He is the gym leader Viridian city
DRagons den you going fight vs the last gym leader from hoenn and the last from the elite four ( they are hard )
you go to blackthorn city to fight the 8th gym leader
you can fight him as many times as you want
Blue is the Viridian City Gym Leader (Badge #16)
his name is morty and he's in Ecruteak city
he is in his gym like a normal gym leader. he is not like misty or clair.
there will be a secret door at olivines lighthouse and it will take you to jasmine then go back to the gym then jasmine will battle you
you never battle her.
you battle them in the dance center after you defeat Claire, the last gym leader in johto
u go to the top of the gym and turn off the waterfall and challenge him.
yes it is in Azalea, but you have to save the slowpokewell before battle the gym leader