In their home realms, ephemeral entities are visible and solid, but in the physical realm the properties of ephemera leave them out of phase in a state called Twilight.
Beings in Twilight are invisible and intangible to anything not comprised of the same kind of ephemera — ghosts can see and touch one another but are invisible to most living people, can pass through solid objects, and don’t even interact with other ephemeral entities like spirits or Goetia. A spirit cannot perceive or attack a ghost, even if they are both in Twilight; it can see the physical world and the denizens thereof, but cannot interact with them. It might follow a human around to feed on the Essence his actions create, but it cannot touch him or make itself known to him.
Many types of ephemeral being can Manifest to affect the physical world. This might involve becoming fully physical, imprinting messages into the world, possessing victims, or just becoming visible. Not all ephemeral entities can Manifest, but even those that can require certain Conditions to do so.
A ghost requires Anchors — the places, objects, and people linked to its living days that reinforce its sense of identity. Spirits need the spiritual Resonance of the area or host to match their own. Goetia cannot naturally Manifest, and must be granted the ability to do so through magic.
Supernal entities remain in the Supernal World, visible only to mages using the correct form of Mage Sight, unless fully Summoned or within overlapping regions of reality like a Supernal Verge. In these cases, they appear fully solid and visible unless they then use their own powers to enter Twilight.
The State of Twilight
Without Manifestations or magic, ephemeral entities in the material world exist in the state of Twilight. To beings in Twilight, physical objects appear pale and semi-translucent; light sources are dimmed, and sounds are distorted. They can only touch and interact with Twilight objects, phenomena, and creatures comprised of the same kind of ephemera.
Attacks pass through a Twilight being, and even solid concrete in the material world is no more hindrance than fog. Sometimes structures and objects can enter the state of Twilight, such as the ghostly reflections of destroyed buildings or items, as well as those made immaterial through magic — these are entirely solid to Twilight entities of the same type of ephemera.
Movement through Twilight roughly corresponds to that of the material world, even though there is no gravity, wind, or pressure. Flight is not possible unless appropriate for the entity’s form; a fiery-winged Goetia might take to the sky, but a clattering, rusting spirit of metal will stick to the material terrain.
Ghosts, ghostly echoes of destroyed buildings and objects, and objects or people that have entered Twilight through the magic of the Death Arcanum are all considered in phase with each other.
Spirits and objects or people that have entered Twilight through the magic of the Spirit Arcanum are considered in phase with each other.
Goetia and mental projections through the Mind Arcanum are considered in phase with each other.
Supernal entities that have entered Fallen Reality and used their Arcana to enter Twilight are in phase with the appropriate type of entity.