You need the Silph Scope, which you get after defeating Giovanni in the Rocket Game Corner basement.
Go to Viridian city and beat Giovanni,the gym leader
Save Silph Co from Team Rocket by defeating Giovanni for the 2nd time, after that you will get the Master Ball! Then you will have access to Sabrina's Gym.
you mainly unlock duelists by defeating a person in duel worlds 5 times but you can also unlock duelists by defeating the gate to the next world or defeating people in CPU mode hope that helps!
In Sliph co., just before the fight with Giovanni, and after the fight with the rival, there is a man that gives it to you
you get it after defeating Giovanni the second time
you get it after defeating Giovanni i believe
in the viridian gym ;)
You can go on to defeat the Elite Four.
he is in the Silph Co building. he is held hostage by Giovanni but upon defeating Giovanni the boss of the company will give you master ball.
Earthquake, Ice Beam, Water Pulse.
you get your first master ball after defeating Giovanni in safron city in the biggest building.
Master ball is with the silph co. chairman talk to him after defeating Giovanni
After defeating Giovanni at his Rocket Headquarters in Celadon City he should give it to you.
the second time you will meet Giovanni is inside the Silph Co building in Saffron City wherein he held the president of the company hostage and after defeating Giovanni the president will give you a masterball for a reward.
Go to Viridian city and beat Giovanni,the gym leader
You need the Silph Scope, which you get after defeating Giovanni in the Rocket Game Corner basement.