Undead are creatures which deny Oblivion's mandate of change. They are creatures which have both been fundamentally altered and yet refuse to change, at least part of their soul stagnated. Those who cling to some physicality, such as zombies and skeletons, often feel most comfortable in The Shadowfell, where the first Undead were born of the most stubborn Shadow Fey. Those who remain as soul remnants, such as ghosts, are typically able to interact with The Ethereal Plane.