As long as the player has Clear Headed equipped to immunize against Confusion, the fight should not be too hard. Since Oeilvert has an anti-magic field, bringing along magic casters will make the battle more difficult, the exception being Quina, whose attack strength varies.
Whether the eidolon and the boss are the same creature is ambiguous. [view·edit·purge]In the Bible, Noah carried seven pairs of each clean animal species and one pair of each unclean animal species, each pair a male and female, into a giant ship called the Ark. The Ark was built by God's command to survive the deluge He sent to purge the world from the sins committed by mankind.