Celestial Marshals themselves are Phantom Demons that exist in the Dream Realm, and they all have the ability to directly enter dreams, just as birds can fly and fish can swim.
Even ordinary Phantom Demons basically have such an ability, as long as they can reach the Material Realm by their own means.
As long as one can enter dreams, they can easily destroy mortals from within those dreams.
Curses, illusions, planting suggestions, modifying memories, or even directly destroying the soul.
After all, mortals are beings that live in the Material Realm, and it is only during dreams that the vestiges of their thoughts project into the Dream Realm.
Apart from professions like the Dream Traversing Monk that possess the "Dreamwalker" trait, mortals have no resistance in the Dream Realm and don't even have a conscious self-awareness.
This is also the essence of certain "Divine Revelations," "Prophetic Dreams," or "Demonic Possessions."
