The sixth gym leader in Pokemon Yellow, Red, and Blue is Sabrina. She is located at the top of Saffron City. There are two gyms, and the one that says "gym gym" is the correct one. There is a really hard maze that you have to go through to battle Sabrina.
You use your strong(est) Pokemon to kill the Gym Leader's Pokemon.
3rd gym
The third gym leader in poekmon pearl is maylene, a fighting type gym leader.
I have Pokemon platinum the 3rd gym leader always their your probaly just not lucky.
In Pokémon HeartGold, you can find the 3rd Gym Leader in Goldenrod City.
Go to the 3rd gym and battle the gym leader and then u found him
The third gym is in vermillion city. The Gym Leader is Sarge, and he uses electric-type Pokemon.
the third gym is in goldenrod city right after ilex forest
The third Gym is the Gym in Veilstone City. You can get there by looking on your map. The leader specializes in Fighting Pokemon.
ground/rock will be good
You have to skip the thied and go to the 4th then go to the third.
I think you get it when you beat the gym leader hope its helps see im at the Pokemon league hard to remember