True Names and Shadows

If a being loses its True Name a skilled mystic can basically magically enslave another being. Magical mind effecting attacks use a partial True Name to get partial results. Animals have fairly simple True Names which is why animals can rarely resist magical mind control and humanoids constantly try to resist magical compulsions. Shadows and True Names are practically the same thing. A shadow is a sort of backup copy of a True Name. A living being that loses its True Name to another person loses its Shadow and sometimes loses their literal shadow. This is why a large portion of people who make pacts with other Fair Folk or spirits have no visible shadow (though not every person who made an otherworldly pact stops having a shadow.
A dead person that loses his or her Shadow is barred from the afterlife, even as a ghost . Void Demons and especially powerful undead can consume a person’s shadow which is why these creatures are so feared. Very powerful mortal necromancers can also destroy a person’s shadow, and it’s naturally considered an especially heinous act. It’s also very difficult. Even necromancers who have no moral compunctions at all cannot casually destroy Shadows. It’s a time consuming mystical feat that is reserved for especially hated enemies.
The undead remnants known as the faceless are the remnants of souls that have lost their shadows. For the vast majority of undead the souls still have a shadow, but their shadow is essentially being held hostage preventing them from having a normal afterlife. This applies to ghouls, wights , allips , degenerated ghosts, vampires, and liches among others.
With zombies and skeletons, the soul still has its Shadow. With undead creatures this simple, only the corpse is used, but the creature’s soul is still free. It’s still considered a grave insult (pun!) to defile a corpse in this manner, but at least the soul isn’t enslaved or held hostage when creating this sort of undead.
Unlike most D&D world, Scarterra has no tried and true method to magically resurrect the dead, but if a mortal mystic finds or knows a deceased mortal’s True Name, it’s relatively easy, all things considered, for a spell-caster to save a person’s soul, even if they were turned into some form of undead. The ritual to use the True Name is pretty easy, but finding a True Name is not easy.
The Shadow is a lot harder to work with, but as long a mortal’s Shadow is intact, at least in theory, the Nine can rebuild a damaged soul.

Nomenclature For clarity, "Shadow" with a capital "S" refers to the metaphysical aspect of a person's memory and a record true name. When presented with a small "s", "shadows" are literal shadows we know in the real world.
Despite being based on a typical D&D world, Scarterra does not have undead monsters called Shadows.

Type

Metaphysical, Arcane