Tips for playing:

Buy many items
Use Deban and Barrier if the enemy is dangerous
Use Saner and Gelun to have an advantage in battle
use skills at certain times of the battle to have an advantage over the enemy
use offensive techniques to hit the enemy in so as to save some skills for the bosses
always have a character who uses shields in battle placed in the front row.
The final boss can be defeated without problems from level 54+ 
(obviously using a suitable strategy, otherwise he will destroy you).
The difficulty level goes up when you reach Zio's Fortress and then goes up again when you reach Air Castle.
It is recommended to have at least all characters at LV 36 before arriving at Air Castle.
Many enemies skills have been modified in both their power and their use.
You will need to use both Barrier and Deban to reduce the damage of some enemies.
Such as the three bosses of Aircastle whose trio ability will inflict physical and non magical damage.
If the mod seems difficult for you, just stop a few minutes to level up your characters.
Balance and Experience, Meseta of Enemies is designed for a player 
who continues the story to have a difficult challenge, 
while a player who stops the story and trains the characters will have a more balanced battle.