The Dark Powers manipulate the domains and creatures within their grasp in the most fundamental ways, controlling magic, the nature of life and death, and the means of escaping from their nightmare realms.
In some domains, magic is an everyday part of life, while in others, insular communities fear it as the province of monsters. Few domains deny magic entirely or outlaw its use, but magic might be rare beyond the spellcasting of local healers or the power of the occasional family heirloom. It's up to the DM to decide how pervasive magic is in a domain, choosing whether a dearth or an excess of magic is more terrifying.
Rarity of Magic. In domains where inhabitants regard simple magic as remarkable, those inhabitants' lack of engagement with the supernatural doesn't mean the DM should limit magic for adventurers. Rather, use this as an opportunity to feature magic-using characters as figures of awe or terror, or to assign storied origins to common magic items.
Corrupted Magic. The Dark Powers influence magical effects, imparting them with sinister qualities. How these changes manifest are for the DM to decide and can shift from domain to domain. Do summoned creatures appear undead in one domain or violently mutated in another? Do divination spells rasp in the voices of otherworldly ancients? Do the effects of drinking a @Potion of Healing feel like grubs weaving wounds shut from within? Magic looks menacing in the Domains of Dread, but descriptive embellishments shouldn't change the actual effects of spells or magic items.
Everyone among the Domains of Dread is a prisoner. The Darklords number among the most prominent captives, but every creature claimed by @The Mists dwells outside the natural order of the multiverse. Even death doesn't afford an escape from the Dark Powers, which hoard every soul that falls into their clutches. In the Land of @The Mists, death isn't an escape, but the beginning of a new terror.
Soulless Shells. Not every being among the Domains of Dread has a soul. Many inhabitants of each domain are creations of the Dark Powers, whose bodies have been formed from the land and @The Mists. For all intents and purposes, and even under magical detection, these beings are what they appear to be. The Dark Powers fashion them as living puppets—individuals who live unremarkable lives that reinforce the status quo, culture, and frustration that torment a domain's Darklord. They tend to be bereft of charm and imagination and to be more compliant and depressed than the others. A woman within the Domains of Dread, soulless or not, can give birth. A child born might have a soul even if one or both parents do not. Conversely, the child of two parents with souls isn't certain to have a soul of its own. People without souls are often, but not always, maudlin folk who experience fear but neither laugh nor cry. If a Darklord of a Domain is defeated and the mists fade, it is possible to leave the Domain, though soulless individuals who do so cease to exist as soon as they exit the border of that Domain. Additionally, most Darklords are able to identify if a person is soulless or not at a glance.
Bright Souls. Individuals born in the Land of @The Mists who have souls tend to be vibrant, imaginative, and ambitious. But they find these virtues stifled by the dour, soulless individuals who outnumber them, leading many to seek better lives and answers to the mysteries of their home domain. Every player's character who was born in a domain is one of these vibrant souls. Only about one in every ten individuals born has a soul.
Death in Ravenloft. When a creature with a soul dies among the Domains of Dread, its spirit becomes caught in @The Mists and can't travel to the afterlife. If a creature who has been dead for at least 24 hours returns to life by way of a spell or other supernatural means, it realizes that its spirit is trapped within @The Mists, likely forever. Using the rules found in the Fear and Stress lore article, the creature gains a new Seed of Fear.
If a being with a soul dies and is not returned to life, that soul remains trapped within the Domains of Dread until it is reincarnated, a process that can take decades. Individuals who inherit the same soul over generations often look alike and might recall memories of their past lives.
Metaphysical Mysteries. The state of souls in the Domains of Dread provides a dose of existential terror to those hoping to manipulate life and death to escape these realms. Beyond that, who does and doesn't have a soul among the domains rarely matters unless an adventure explores themes of life, death, and reincarnation. Players might create ties with long-dead individuals using Dark Gifts and backgrounds. But overall, spiritual stagnation in the Land of @The Mists is meant to provide the opportunity for grim revelations, not existential bookkeeping.
Each domain is its own demiplane, isolated from all other planes including the Material Plane. No spell—not even Wish—allows escape from the Domains of Dread. Spells such as Astral Projection, Plane Shift, Teleport, and similar magic cast for the purpose of escaping a domain simply fail, as do effects that banish a creature to another plane. These restrictions apply to all other effects, including magic items and artifacts that transport or banish creatures to other planes. Magic that allows transit to the Border Ethereal, such as the Etherealness spell and the Etherealness feature of @Ghosts, is the exception to this rule. A creature that enters the Border Ethereal from a domain is pulled back into the domain it left upon leaving the Ethereal.
For the purpose of spells whose effects change across or are blocked by planar boundaries (such as Sending), each domain is considered its own plane. Magic that summons creatures or objects from other planes functions normally, as does magic that involves an extradimensional space. Spells cast within an extradimensional space (such as that created by Magnificent Mansion) are subject to the same restrictions as magic cast within a domain.
While in the Domains of Dread, characters who receive spells from deities or otherworldly patrons continue to do so. In addition, spells that allow contact with beings from other planes function normally, with one proviso: the domain's Darklord senses when someone in their domain casts such a spell and can choose to make themself the spell's target, so that they become the one who is contacted.