With your pokemon. (Flying or Psychic are the best types for Fighting pokemons).
bet every gym but the last
She is in Hearthrome City, in Platinum she is the 3rd gym leader.
it's the 3rd badge!
In Ruby, Sapphire and Emerald, the 3rd Gym Leader is in Mauville City and in Diamond, Pearl and Platinum, the 3rd Gym Leader is in Veilstone City.
im not sure but i know it is to go to canalave city or go to the hearthome city.
The fourth gym in platinum is the veilstone gym
Just the way between Vielstone (3rd Gym) to Pastoria(4th Gym)
You use your strong(est) Pokemon to kill the Gym Leader's Pokemon.
The Hearthome City gym is a Ghost-type gym which is the 5th gym in Diamond and Pearl and the 3rd gym in Platinum. The gym leader is Fantina, who uses a Drifblim, Gengar, and Mismagius in Diamond and Pearl and a Duskull, Haunter, and Mismagius in Platinum. Defeating her gets you the Relic Badge.
Well,the 3rd gym leader is maylene. She is also gym leader number 3 in diamond and pearl.So no need to worry.
The third Gym is the Gym in Veilstone City. You can get there by looking on your map. The leader specializes in Fighting Pokemon.
I have Pokemon platinum the 3rd gym leader always their your probaly just not lucky.