And you could come up with a description like this for the monsters. For example, they lived in the darkest corners of the dungeon, were terribly fierce and frightening (you could even add fear to their abilities if it doesn't become overpowered), and ate everyone they could. However, later, the Necropolis learned to control their minds and use them as a serious assault unit. Or, as another option, they could be the result of failed Necropolis experiments. (but that might be too much).
And you could come up with a description like this for the monsters. For example, they lived in the darkest corners of the dungeon, were terribly fierce and frightening (you could even add fear to their abilities if it doesn't become overpowered), and ate everyone they could. However, later, the Necropolis learned to control their minds and use them as a serious assault unit. Or, as another option, they could be the result of failed Necropolis experiments. (but that might be too much).