"That thing is looking at us… doesn't it?" Priscilla spoke as she naturally stepped back.
Her spells and mystical items don't work well with a possessed person. At most, she could use her movement spell to run away.
As for Philip, he also had a terrible match-up against such a being. He had a Blood Curse Spell and Severe Ailment Spell, but they're not going to work well against a possessed person.
He can use his Lesser Corruption Sword Armlet against it, but it is still on cooldown today.
After their battle against Terrence's group, his formed sword was destroyed and needed some time to recover. Furthermore, even if it works, the Darkness Sword may not necessarily be enough to deal with the thick-skinned butcher.
Furthermore, according to their studies, a possessed person would normally have 3 or 5 times their strength and would also have resistance against lower-tier Spells.