This trick is only available near the end of the game. Once you return to Elicoor the last time visit the outfitter in West Peterny. Check to see if the item Durian Stun Bomb-R4 has been invented. If not you might have to invent it yourself.
Once the shop has the item, buy 20 of them. This should be about 200,000 fol. Don't worry though you'll get that back and more. After you have 20 bombs, head to Irisa Plains. There will be the white winged monsters roaming the field. Go up to one and start a fight. As soon as you can use items, use the bomb. Instant Win.
Now in order to get a ton of EXP and FOL you need to get in a battle a make a bonus battle occur and win. After this happens repeat the bomb trick. When your chain starts to have 300% and 200% fol, you will see the trick at it's best. With two of the white winged monsters defeated at once you gain about 12,000 EXP and 33,200 Fol. When you run out of bombs, go to Peterny, buy some more, run back, then repeat.
This trick is ideal for people who want to level up to very high levels in a short amount of time, collect hard to get battle trophies, level up low level char, get lots of Fol. An example I will show is that in about 5 minutes I got a level 1 character to level 40.
