outside of Mauville. you go south to the the water and use surf if you have it and west. there you will find land that leads to a cave, in that cave is New Mauville use the Basement key given to you by the Gym Leader of Mauville and you are there.( there are some Pokemon that can only found there polemon like Voltorb, it's eveoled form Electrode, magentmite and it's evoled form magenton.
Head south of Mauville, towards the entrance to cycling road. Surf across, and head west. You'll eventually find a cave. That's New Mauville.
magnetons cannot be found in the wild, however you can find a magnemite in new mauville just outside of mauville
After you beat your dad, go back to Mauville. You will see Wattson standing outside. He will ask you to shut off the generator in New Mauville. After you do that, return back to him. He will thank you and give you the TM thunderbolt.
The day care center is on route 117 between Mauville City and Verdantuf Town.
Randomly you can receive some from the berry masters wife there house is in the route east from mauville city.
where ever ya left it
Head south of Mauville, towards the entrance to cycling road. Surf across, and head west. You'll eventually find a cave. That's New Mauville.
Go just south of mauville to the entrance of the bike trail, just below the bike road is a fisherman, and on the right of the fisherman is an entrance to the 'lake', go on the lake and go south a tiny bit until you get to an island, from the island, surf right under the bridge until you see a cave entrance, that's the entrance to new mauville. I have sapphire, so somethings may be a bit different, but not too much, enjoy!
you get it in the NEW MAUVILLE basement
From Mauville City, go south, you'll meet the Fisherman. Surf and keep to east. Then, you reach the New Mauville.
magnetons cannot be found in the wild, however you can find a magnemite in new mauville just outside of mauville
it is in mauville city it is in mauville city
Go south until you are below and out of Mauville City, and Surf in the water until you find a cave: That;s New Mauville.
In Pokemon Sapphire when the player defeats Gym Leader Norman in Petalburg City, Wattson, the Gym Leader of Mauville City can be found at the intersection of Route 110 and Route 118. Upon talking to him, he will give the player the Basement Key to access New Mauville City.
You get the third badge in sapphire when you get to Mauville. You have to battle Gym Leader Wattson in the Mauville City Gym.
At new mauville after you beat your dad go to wattson and he'll give you directions
I believe wattson the 3rd gym leader gives it to you after shutting down the generator in new mauville.