In Pokémon Sapphire and Emerald, after going to Mt. Pyre, you have to go to Lilycove City and enter Team Aqua's Hideout.
Battle and Get Items
In the entrance of the hideout, you see a Grunt running around. He has two level 32 Poochyenas. After the battle, go north to reach the next room.
Step on the white circle on the right to find a Max Elixir. Step on the circle again to go back to the first room, then step on the upper white circle. Afterward, go through the north door.
Go east and you will find two grunts. The girl has a level 31 Poochyena and two level 31 Carvanhas. The guy has two level 30 Poochyenas, a level 30 Zubat, and a level 30 Carvanha. Go southwest from those grunts and step on the white circle.
There are many teleporters here. First, step on the upper-left one. Then step on the middle one. Then step on the left one. Finally, step on the bottom-left one. You will end up in a room with four items on the left side of the room. Two of these are Electrodes, one is a Nugget, and one is a Master Ball. This is the only chance to get these items, so be sure to get them now.
When you are done in the room where you got the Master Ball, step on the white circle. Then step on the right circle, then step on the middle circle, then step on the right circle, and finally step on the circle in the top middle of the room. In the next room, step on the other white circle to return to the large area with the two grunts on the east side. Go to the far right of the room and step on the white circle there.
Go through the north door. Go south and then west to find a white circle. Step on it and go left to find a Nest Ball. Then go to the right and step on the circle. There is a grunt running around here. Go east and step on the circle, then go through the north door.
There is a grunt in this room. Go to the east and through the door. Go south past the grunt and step on the white circle here.
Go southwest and you find Aqua Admin Matt. He has a level 32 Carvanha, level 32 Mightyena, and level 32 Sharpedo.
After you defeat Matt, go southeast to find another white circle. It takes you back to the entrance of the hideout. Leave the hideout.
When you go outside, you discover that you can now Surf east to Route 124.