The thunder plains is full of lightning bolts your party must dodge when passing through. But along with having to dodge it comes a sidequest where you can get various items! Getting items depends on how many times your character can successfully dodge the lightning in the area. In order to dodge the lightning you'll need to press the X Button just as the screen flashes. If you are successful your character will not get hit, however, if your timing is off they will get hit and have some HP depleted.
If you do happen to dodge is so many time, as shown as on the list below, you'll be able to obtain a prize at a chest outside of the Travel Agency on the plains. You can also check how well you are doing inside the travel agency on a small book.
Dodges
Prize
5
2 X-Potion
10
2 Mega Potion
20
2 MP Spheres
50
3 Strength Spheres
100
3 HP Spheres
150
4 Megalixirs
200
Venus Sigil
Even though you'll want to dodge lightning, if you do happen to get struck a certain number of times you can also recieve a small item. For getting hit with the lightning 30 times you'll recieve an Ether, and for eighty you'll obtain an Elixir. The effort to do it, however, really isn't worth it.