All enemies in this fight are weak to area attacks, but they also use a lot of area attack.
Mindflayer can use an area attack with a chance to paralyze, and also has an attack that can inflict poison. Units with high faith might have trouble if you don't give them some paralyze resistance.
Netherworldly Crimson Orb, Bloody Moon helps with getting resistance against area attacks.
Magic Attack Up, Silence Res Down, Accuracy Up, Unit Attack Res Up, Area Attack Res Down
Pierce Attack Up, Accuracy Up, Unit Attack Res Up, Area Attack Res Down
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Omega Raid Boss Event