It is the first Angeal copy that Zack encounters. This foe has a Jump attack which may inflict moderate damage, depending on Zack's current stats. To avoid his Jump attack, wait until it is mid-air, then dodge quickly. Try dodging to stand behind the A-Sahagin, allowing Zack to attack from behind, causing a large amount of damage, which should defeat the enemy, with multiple hits. If that fails, repeat.