A Nightmare has the shape of a fear, and so no two are alike: a thing of too many legs, a figure with a known face gone wrong, a dog that is mostly teeth, a shape at the end of a corridor that is always a little closer. What they share is distortion. Proportions are wrong, limbs bend the wrong way, and their surfaces are shadow, flesh, and something in between, shifting as one looks. They are often silent until they speak, and then they speak in the voices of people the dreamer knows, saying things those people never said. The smell is whatever the dreamer dreads: smoke, sickroom, rot.

In the Nexus they are grotesque and solid, made of shadow, flesh, and nightmare logic, and the fears of different dreamers merge into worse things than any one could make.

They arise throughout the Dreaming Veil, wherever a dreamer’s fear takes hold, and fill the Nightmare Nexus, which wakes in places of mass trauma and great fear. A nightmare-beast on the Material Plane is rare and does not last unless something holds it.

They hunt. A Nightmare stalks, taunts, and corners its prey, and uses the dreamer’s own memories and insecurities against them. It hunts dreamers who are unaware they are dreaming above all, and a lucid dreamer is harder prey. In the Nexus they have no society and exist only to feed on fear; they are relentless and adaptive.

They are not alive in the ordinary sense; in the Nexus they are psychic constructs, and ordinary weapons do little to them. They can be harmed only by the traveller’s will, or by breaking the dream. What they do to a dreamer can cause trauma or death in the waking world. A nightmare-beast made real by a dream hunts fear more reliably than flesh.

What the Nexus gives a body stays solid when carried out: the hide, teeth, and bone of slain Nightmares can be worked like any other material, and are. Facing one in the Nexus, and overcoming the fear, is said to grant immunity to that fear in the waking world. Their danger is death, in dream and out of it.

On Caeldon nightmares are blamed on many things, bad food, a curse, the dead, and travellers and dream-guides know that some of them are something more. The advice of the dream-guides is the advice of the Dreaming Veil: keep reminding oneself that one is dreaming, and never fight a Nightmare one cannot wake from, but run, or wake.

Dream-guides still speak of one of their own who went into a dying lord’s nightmare to fight the thing killing him and came out with its claw-marks on her waking face.