Easy XP/quick leveling
When you reach any new dungeon, find a save point. Use a combination of Mirage abilities, Seeds, and Mirajewels to create abilities that directly counter those of the dungeon you are in. For example, in The Sunken Temple dungeon, the enemy Mirages are mostly water type. Put Ramuh into your stack and make sure he has a lightning ability that hits all targets (Thundaga, Judgement Bolt, etc.). Fighting near a save point allows you to completely refill your HP and AP after each battle. Simply get into a fight and perform your most powerful elemental attack that hits all targets and quickly kills them. After each battle, go to the save point (you do not have to open the menu) to refill your HP and AP. Repeat this process as many times as desired.