The cave Wattson, the Mauville City Gym Leader, tells you to venture inside is New Mauville. He wants you to turn off the generator inside New Mauville. It appears to be acting up and causing problems for people in Mauville City. Inside New Mauville are various items and switches that allow you to navigate through New Mauville and reach the generator. There is also wild Pokemon in the power plant like Magnemite, Voltorb (Three fake items are Voltorb), Electrode, and Magneton. To reach New Mauville you must head south of Mauville City and use Surf in the lake located in Route 110. Surf below Cycling Road and you will see a cave entrance. That is New Mauville. To enter the power plant, it requires the Basement Key (Which Wattson gives to you after taking the request). Hope this helps.
Fortree Gym leader
after beating the 4th gym leader may/brandon will come to you and give you the goggels
by beating the fourth gym leader
keep using phychic
the closest you can be to a gym leader in this game is setting up a secret base with your best Pokemon then mixing records
If you mean "Is Juan the leader in Pokemon ruby?", then no. It's Wallace who's the leader. Juan is leader only in Pokemon emerald. The champion is Wallace in Emerald, but Steven is the champion is Ruby and Sapphire.
marshtomp
Fortree Gym leader
He is the Pokemon League Champion.
after beating the 4th gym leader may/brandon will come to you and give you the goggels
After you beat leader Norman
flannery
Help me
Water Gym Leader
Go to Sootopolis.
Beat the gym leader
The Pokemon league!