Corruption
The Staff of Epos was an Ancient Artifact that adjusted to the wielder's power. It was capable of sealing the Soultraits of all targets in its range.
That would have been useful to know before the Undead Pharaoh sealed Michael's Soultrait. The only advantage was that his 7-Star Soultraits hadn't been sealed. Only Divine Lifeform could unleash the Staff of Epos' true power. The Undead Pharaoh might have been a Divine Lifeform when he was alive, but his power was still sealed. He could only seal a portion of Michael's 7-Star Soultraits using the Staff of Epos.
Nonetheless, that was enough to put Michael into a tricky situation. He couldn't escape the Undead Pharaoh's grasp because he was in the pharaoh's throne hall, which had been locked moments after Michael emerged.
The only reason Michael didn't panic was that he had the World Serpent and the Curse on his side. If not for their presence reassuring him, Michael would be on the verge of losing his sanity.