Simple
step 1:have the 2nd badge in dewford town
step 2:tell to the guy near a blueprint inside Stern's shipyard that you will bring the Devon goods to Stern
step 3:deliver the Devon goods to Capt. Stern
step 4:defeat the 2 magma/aqua grunts
step 5:walk to route 110 and battle rival
walk,walk,walkuntil you reached Mauville city
P.S.:to gym inside the gym battle wally first
he uses ralts so use a dark type
Defeat the 3rd Gym Leader, Wattson, in Mauville City.
The fifth gym is in petalburg city
The gym in Petalburg.
In the lavaridge town gym.
you cant
The third gym leader in Pokemon Sapphire is Wattson and he is located in Mauville City.
it is on mauville city
that electric type guy
Fight Wally who is by the door
Magnemite,Voltorb,and Magneton.
You get the third badge in sapphire when you get to Mauville. You have to battle Gym Leader Wattson in the Mauville City Gym.
the third gym leader wattson.
Ahead North of Mauville, you go to Mt. Chimmney
Defeat the 3rd Gym Leader, Wattson, in Mauville City.
it is a dragon type Pokemon gym
fire gym in lavaridge
In sapphire, the 5th gym leader is your dad, in that city after Oakdale.