Thunder Plains - South
The team will enter the Thunder Plains after having completed the events at Guadosalam.
It is possible to get struck by lightning while traveling through this area. Press the Button when a lightning strike flashes on the screen and you can dodge the lightning and take no damage.
Grab the treasure chest to the left of the Save Sphere to obtain two Phoenix Downs. Save your game before you continue. There is another treasure chest to the northwest of the Save Sphere that contains two Hi-Potions.
Continue following the wall on the west side of the map and you will find a treasure chest that contains 5,000 gil. It is just behind the glowing cactuar statue which is reads “A strange stone” if you touch it.
There is a chest in a small walkway on the east side that contains a Water Ball. Equip this item if you are using Wakka as the Waterstrike ability is incredibly powerful against the Lightning-based enemies in the Thunder Plains.
Further on down the pathway you will run into Shelinda. Keep going until you reach the end of the pathway and hit the Thunder Plains Travel Agency.
Thunder Plains - Agency
There is a book on the counter that looks like an Al Bhed Primer but it is actually a storybook called “The History of Summoners, Thunder Plains Edition". It will tell you a little bit more about the strange rocks with the Qactuars on them.
Save your game at the Save Sphere and then talk to Rikku. Speak with Rin once he enters and he will ask you “How goes your study of our language?”. Select “Okay” and he will give you the Al Bhed Primer (Vol. XIV). Go back to where Yuna went, towards the back of the agency, to continue the story.
Talk to Rikku again in the morning and then the group will exit Rin’s Travel Agency. You will notice that there is a small glowing item on the shield. Examine it to receive a Yellow Shield. If you don’t already have a Yellow Shield equipped to Tidus equip this one to him now. Tidus will now be immune to lightning-based attacks.
Tidus will barge in to Yuna’s room for another short scene. Afterwards, it’s time to continue the journey through the Thunder Plains.
Rather than going north, head south back into the area you previously came from. You will notice that there are two ways to go north from here (and the red arrow will be pointing to the second exit. Go north through the other pathway.
Thunder Plains - North
Directly to the right when you come from this pathway is a treasure chest that contains an X-Potion.
You could potentially run into Iron Giant fiends in the second half of the Thunder Plains. These fiends are particularly powerful but are great to level up against. Use Auron’s Power Break ability to heavily reduce the amount damage that they deal to your party members. You can also use his Armor Break to reduce their armor and take them down a lot easier.
Continue northward until you reach the Save Sphere and save your game. Half way down the pathway Yuna will interrupt the journey for a bit more dialogue and story. Yuna will announce that she’s decided to accept Maester Seymour’s marriage proposal.
There is a treasure chest on the left side of the path that contains an Ether. It’s just behind the structure where the dialogue takes place. And to the right side of the pathway is another chest that contains 2,000 gil. Use the screenshots to help you find them.
Keep going until you reach the Macalania Woods.