Mario & Luigi: Superstar Saga/Oho Oasis, Oho Ocean and Beanbean Airport

Oho Oasis (Thunder and Fire Temples)
Fortunately, this time you're sent directly to the next location. In this small island, is where the Fire and Thunder temples are located.

Thunder Temple


This is right upwards from the place you are when you get to this place. Enter the temple, and then enter another room from the upper left corner. Here you want to move to the room on the right, and you'll have to use Luigi to advance through the steel gate. Then move forward and you'll enter another room. In this room, use your hammer to destroy the wall with a lightning on it. After the guy says he has no business with you, head to the lightning orb and interact with it. Afterwards, you'll learn to use the Thunderhand. Then, go to the room to your lower left, and in that room use your new ability to electrify the orb that needs power. You can now reunite the bros.

Fire Temple


From the place you start in move left. Now enter this temple. If you did the thunder temple before, this is the exact same but inverse. Head to the room with the fire orb with mini Mario, then smash the wall blocking your way. Wait for the guy to stop talking, then interact with the orb. After you learn the Firebrand, head to the lower right of the room, and in the next area lit up the spot that needs fire. You can now reunite the bros.