If you are talking about Jasmine you just need a fighting type pokemon or a pokemon that knows a fighting type move. Or a fire pokemon or a pokemon that have fire type move is fine. And if you are talking about Sabrina she is a psychic type master so you will need a bug/ghost/dark type pokemon or a pokemon that have the move type.
You kill the Gym Leader's Pokemon with your Tepig.
After you've beaten the 6th gym leader Byron, you'll have to go to Snowpoint City via Mt. Coronet. At this city you can find the 7th gym.
beat all gym leaders
you have to of beat the snow point gym leader you have to of beat the snow point gym leader
after you beat the viridian gym talk to him again and he'll leave and voila!! you get ur own gym
Beat the rest of the gym leaders first.
Primarily beat the gym leaders and beat the elite four
lv 30
Go south to the next gym.
clainwood
ponie
Yes, beating the 7th Gym does not effect getting the secret potion.
You have to beat all of the gym leaders in Johto then look at the map.
afther you beat all the johto gym leders.
you need a physic type
You go around map. beat the gym leaders and collect pokemon. battle other people and level and evolve your pokemon.
beat all the gym leaders. Hope this helps!