Trainers can be challenged to a rematch in "fire red" by using the item the "Verse Seeker". It will check it all the trainers currently on screen would like to battle. This time they will be slightly stronger than before, so be prepared. The VS Seeker can be very handy when training for a gym battle or the Elite Four.
Brock and a few other weak trainers
You get money by selling items or beating other trainers in a Pokemon battle
first u must get Pokemon navigator(pokenav) from rustboro city and u must register other trainers when u fight then after u beat elite 4 , u must see your pokenav and if u see a poke ball next to the trainer in ur pokenav in matchcall it means u will fight him again
Travel around sinnoh
If you want to you can try the other modes like single or knockout. Not your thing? Train more Pokemon and get all the Pokemon in the pokedex. And meet some other Pokemon leafgreen and Pokemon firered players.
you can do anything on the game like beat trainers again and other stuff.
No. You can battle wild Pokemon, trainers in the game, or battle a friend using the MultiPlayer link cable feature.
Make sure both your trainers are at the same pokemon centre
Once you have defeated him in battle there is no other way to fight him again unless you saved before the fight with heatran.
Seven island has not much to offer in the north there is a trainer tower where you can test your Pokemon against other expert trainers. Also in the south you can capture Unowns in the tanoby chambers. Also this island is home to strong trainers this is a good area to train your Pokemon.
He is actually the second gym leader, but you can only fight him after you beat all the other gym leaders. After you beat him, you can fight the Elite Four. PS: He is in Viridian City.
Team Galactic and other Trainers.