Undead

Undead share many traits with golems, and the magic used to animate them is similar. However, the physical structure of an undead is already there, and designed to move in a way the creator is familiar with. Depending on the state of the brain, there are already some good existing patterns to reuse. The creator combines these resources with a framework and set of commands stored in an ethereal cloud known as a ghost.

A ghost embedded back into a physical body produces a decay-inhibiting system. The undead do need to eat, but if they go too long without food they merely fall into torpor wherein they wait for food to wander by. In torpor they've only vague visions and scents to alert them to passing prey, and if they remain in this state too long they risk being locked in, released from their own whispers only after years or decades have slowly drained the last wisps of vitality from their shells.

Incorporeal undead are ghosts given greater volumes of ether and activated. They are notoriously difficult to control or contain, and so are quite rare compared to their corporeal counterparts, used mainly as weapons of terror by cults or rogue borderlands.

In both broad classes of undead, a human consciousness has been co-opted and damaged within each undead. They have an innate rebellious quality - more active and dangerous undead also tend to be more free-willed. They are constantly reliving shattered bits of memory, trying to add 2 to 2 to find it comes up to orange, while shattered senses and maddening glimpses of the past cause them to lash out in confusion and torment at any life.

Undead can also occur spontaneously when a ghost isn't destroyed with its host and moves on to another. There is a physical network responsible for reanimation, and knocking the body immobile doesn't always destroy that without something like... fire. There are dark legends of self-replicating ghosts, and some sages believe such a thing could have been one of the unspeakable aspects of the slow burn, which may still linger on in any of the haunted ruins of the great cities.