In the Thunder Plains, if you can dodge the lightning a certain number of times in a row, you will be rewarded with items. Additionally, if you get struck by lightning 30 times, you get an Ether. If you get hit 80 times, you get an Elixir.

Times Dodged Item

5 Two X-Potions
10 Two Mega-Potions
20 Two MP Spheres
50 Three Strength Spheres
100 Three HP Spheres
150 Four Megalixirs
200 Venus Sigil