Cairo controlled the shadow servants and their bodies sink into the ground. This magic can help Cairo kill people even if he's a bit far from them
The shadow servants have decent hiding skills but it still has a lot of flaws. Even though the shadow servants can sink their bodies on the ground, their magic fluctuation is still not that fully hidden. Also, they can be noticed too due to the ground having a dark color if they entered it
Cairo is still only a mere Mage, his magic has limitations and flaws. If he further advances in ranks then he can definitely do something about the flaws of his magic
However, the current shadow servants are still enough. This is also one of the reasons why Cairo chose to strike at night. With the protection of the darkness of the night, it would be harder to notice the shadow servants
