As the title implies, I'm trying to find the least time-consuming way to level up my characters or find an area with higher encounter rates for Grow Apples.
Grow Apple and Super Grow Apple are rare encounters that can be found in any 3-floors dungeons.
These guys like to run away so make sure you use Shut Out as soon as you find them. After that, use Arnaud and Yulie's magic (Ley Boost, Hyper, Slow Down, Fragile, Quick) to boost up Jude's attack power and RFX while weakening and slowing down the enemy. Then unleash Jude's Assault Buster for some huge damage (don't forget to use a Lucky Card and Mystic). If you did this right, you'll gain a lot of EXP.
I recommend giving Arnaud both Speed Skates and a Tiny Flower (the equipped character will begin their first turn in "Detonation!" mode, raising all of that character's attributes) to wear. This will greatly increase the chances of him acting before the Grow Apple. Also, Equip Jude with Cat's Paw badges to help further increase his damage output.