Undead

The first part of this process is to acquire a suitable soul for reanimating the body. Souls of most creatures stay anchored to the body for a while after death, unless the body is totally destroyed, but after that they move on to the spiritual planes and are beyond the reach of mortal necromancers. Thus, extracting a soul from a body that had died a long time ago is not possible.  A necromancer needs access to the recently dead to capture the souls they need to practice their craft. Getting access to the dying in their last moments can be tricky, so most necromancers resort to producing their own recently deceased corpses (through killing).

Once a necromancer has one or more souls captured and ready for use, they need a suitable body. A soul can only serve as an animation core for a body that is similar to the one it once inhabited, so one cannot use animal souls to animate humans and vice versa. Obviously, the quality of the animation is the highest if the necromancer uses a soul that was originally matched to the body in question, but any human soul will do to animate most human bodies.

The body that is to be animated is typically put through a preservation process to stop it from rotting, as it will not last very long otherwise. Despite this, most zombies will break down over time, depending on how intensely they are used, how good their preservation is, and how hostile the environmental conditions they operate in are. Skeletons tend to last longer than zombies, but also tend to be weaker and less dexterous, as the soul is meant for controlling a body of flesh and not one of bone.

Despite some fanciful depictions in stories, zombies do not shamble and stumble about – they move with the speed and coordination their living forms once possessed. They are still as mindless as any other golem, however, and do poorly if left to execute orders without supervision.

The souls that animate the undead have another function beside being cheaper than a constructed animation core – they are sources of mana, meaning undead always have their own power sources. This makes undead easier to use outside of magic-rich areas than regular golems.

Despite its many advantages over classical golem making, undead creation is seen very unfavorably in most places. Necromancers desecrate the bodies of the dead and enslave their souls, which makes their actions completely taboo for most people, regardless of possible efficiency gains. Priests in particular hate the practice, as the gods pronounced it extremely blasphemous while they still talked to people. Any country that tried to legalize necromancy would inevitably find itself a target of a coordinated holy war from all their neighbors.

It is possible to animate a corpse with the aid of an animation core. Using a corpse instead of an artificial puppet cuts down on the costs somewhat, and is often not outright illegal in the same way real necromancy is. On the other hand, flesh golems carry many of the same stigma that regular zombies do, regardless of what the law says, and flesh is not a terribly good material for golems. As such, flesh golems are rather rare, even by golem standards.

Particularly capable necromancers will sometimes make sophisticated flesh golems by fusing various corpses and body parts together, often drawing upon corpses of different magical creatures and incorporating non-biological parts into the construction. The resulting body is too different from its component parts to be animated with a soul, and requires an animation core to function properly. Souls may be used in the construction regardless, in order to help power the thing.