~Dodge 200 lightning strikes and obtain the reward~

This trophy can be very difficult, but also easy depending on how you approach it. Once you enter the Thunder Plains, you'll have lightning coming down and striking you randomly; you'll need to press X(EN)/O(JP) to dodge the lightning when you see the screen flash white. If you press it fast enough you'll dodge the lightning, if not you'll get struck; you'll need to dodge 200 consecutive strikes and get the reward to earn this trophy. You'll have to count your dodges as the trophy is only rewarded once you get the item for 200 consecutive dodges. Keep in mind you can't leave the area or use the save sphere to keep your dodge count.

Before you attempt this you should get a piece of armor with the No Encounters ability; attempting this with random battles is nigh impossible, but also speeds up the process. Now on the left side, near the middle of the southern half of the Thunder Plains is a crater; there's a lightning tower just south and a little niche to the east. Every time you approach this crater lightning will strike, approaching the crater literally forces the game to send a lightning strike. You can dodge this strike, then take a few steps away and go back towards the crater to force and dodge another lightning strike.

This method is not only effective and relatively safe, it helps offset the upscale lag input. The HD version has lag input and so with a random lightning strike even if you see the screen flash white, you'll probably be too late to press the button to dodge. By using this area you can compensate for the lag and press the button at the right time to dodge the lightning. If that's not going well for you and you have an older model TV, you can swap out the HD/PbPrG cables with AV cables to get rid of the lag.

Once you've dodged 200 (or more) lightning strikes, head to the Travel Agency that's between the North and South halves of the Thunder Plains. There will be a chest outside with various items for your lightning dodging prowess. The final item will be the Venus Crest / Fire Star Holy Seal for Lulu's Ultimate Weapon. Once you get that item you will earn the trophy.