The first half of the battle the enemy will increase its elemental resistances to the attack it is struck with. Then, in the second half of the battle it will shoot powerful elemental attacks from multiple body parts.
As the elemental resistances it increases in the first half will persist to the second half if not removed, managing the elements with which to attack is critical.
Also, the enemy's stats will be buffed in the second half of the battle depneding on which body part is taken out, so be sure to work out a strategy on the order in whcih you defeat them.