I got bored and decided to share my strategy for leveling up easily.
NOTE: This strategy does not work as well for Dream Eaters.
The Leveling Spot
The place we want to go is Symphony of Sorcery. Go there via the Chamber. Now go down stairs and outside. Here is where we will level grind, but first, you need a good Command Deck. Here are some useful Commands.
*Only if you have Exp Boost. Used to easily get Riku's HP to the Alarm Zone.
Next, set up your abilities to help level up quicker:
Activate: EXP Boost (Keeba Tiger, Drill Sye, Cera Terror) EXP Walker (Skelterwild) Second Chance (R & R Seal, Meowjesty, Escarglow, Zolephant, Aura Lion) Once More (Drak Quack, Tyranto Rex)
Deactivate: Treasure Magnet EXP Zero (Obviously)
Next, lower your HP to the alarm zone to get 2x EXP if you have EXP Boost (Riku can easily do this by spamming Sacrifice) and unequip any Treasure Magnets you have on so you don't pick up as much HP Balls.
Les do Dis!
Now, just enter and exit the tower, taking out the dream eaters easily with commands such as Mega Flare or Meteor. (Avoid using Salvation and Faith as they restore HP) If you have EXP Boost and you're in the alarm zone, you will get around 2000-3000 EXP everytime. (You should level up every 2-5 minutes)
Some Helpful Tips
Try and get Magic Gain Lv.3 / Attack Gain Lv.3 so you can defeat enemies faster thus getting EXP quicker. Maybe also get Drop Decelerator Lv.3 and avoid the Risky Play Weather Forecast so you have more time to level up with each character.
The amount of EXP to 99 (Incomplete)
Sora: 786800 Riku: 786907
Original Post: http://kh13.com/forum/topic/38889-level-up-easily-in-kh3d-guide-spoilers-and-stuff/