Lich

Liches are undead that bind their souls to phylacteries and then use the phylacteries to generate physical forms. As such, demons seem to be liches themselves, as the demons that fill the ranks of the Nether have their spirits tethered to the Nether. 
Lich creation is nearly always linked to demons, who master the rituals behind creating Phylacteries. A demon's chaotic energies can rip apart and remake beings in the Nether as skeletal liches. 
= Lich ritual =
The basic idea is that the process involves making a deal with a powerful demon/evil god. The ritual includes ripping out the soul and binding it to a phylactery; this gives them Resurrective Immortality, as when destroyed they will reform from the phylactery unless it is destroyed before they do so.
Becoming a Lich implies removing all the blood from the body and replacing it with something else (sometimes health potions). It also includes placing the soul of the lich into an object. The soul can be divided into several parts. Splitting the soul requires a murder to take place. When split, it is often into 7, 8, 10 or more, extreme cases can go up to and beyond the 100’s of splits. Sometimes, the splitting causes the different parts to be aspects of the Lich’s original personality.  
= Phylacteries =
Phylactery creation is a demonic ritual usually reserved to binding a demon to an object outside the Nether realms. This allows the demon a permanent presence outside of the Nether as long as the object isn't destroyed. Should the demon be killed, the yeast will eat at its body until almost nothing is left. It will then warp itself to the object (or if it doesn't have one, it's original tether point in a sphere of hell) and begin its rebirth. 
Liches are basically non demons who have learned to and successfully created a phylactery for themselves, usually by learning or from a demon. 
Phylacteries are objects designed to contain the soul of the Lich. Basically, the object contains detailed instructions on how to recreate the Lich previous body. When the lich is killed, the yeast will warp to the tether point, the object, and commence rebuilding the Lich from these instructions using whatever nearby materials are available thanks to telekinesis. 
While the body is being rebuilt, the lich is “hibernating” meaning the yeast is collecting the required materials to rebuild the body. The materials are stored into three large jars (the jars that originally contained the lich's blood when it metamorphosed). If they are emptied, or otherwise destroyed, the lich dies.
The resurrective immortality is not infinite however, it consumes the soul bit by bit until the lich is finally destroyed. The exact number of resurrections possible isn’t known. This has led to the budding profession of Thanatonaut Liches, who spend their days holed up in a lab with a notepad and a gun with which they kill themselves over and over and then describe the experience when they revive.
The type of object chosen to contain the lich influences the ritual. For example, if maggots are chosen, the body must be consumed by said maggots for them to reform the body once the lich is killed. Another example, if a bottle is chosen, its contents must be drunk and cause the death of the future lich. 
= Feeding =
A lich needs to "feed" once a century by way of a mystical rite that involves murdering a sapient humanoid and stealing its heart before magically burning it into powder, which it sprinkles on itself. A lich must consume at least one soul every year in order to preserve itself. 
== Becoming a Lich has advantages ==
Undead command: They are naturally gifted at advanced necromancy, allowing them to manipulate the undead to do their bidding. 
Fountain water blood: They have their blood replaced with fountain water, which prevents them from taking long term damage. 
Spiritual Possessor: A lich can summon spirits from the moon to possess beings. 
Telekinesis: Courtesy of their demonic powers, Liches have telekinetic powers, the most obvious one being that they typically float a few centimeters off the ground. 
=== Becoming a Lich has drawbacks ===
Skeletal figure: Fountain water stops muscle growth, resulting in liches invariably becoming emaciated, bone thin and downright skeletal beyond recognition over time. 
Unappetizing leftovers: The lich's bone thin physique also prevents yeast from consuming the body, since there is little to eat, meaning liches leave behind mostly intact corpses. 
== Effects of being a Lich ==
Undead creation: A lich powerful enough can raise the dead simply from its presence by emitting yeast that raises the corpses.
Demonic presence: Being in the presence of the Lich can cause those nearby to mutate and adopt demonic, animalistic features. For example, seafaring lich crews tend to develop sea creature features. 
== Species of Liches ==
=== Dalmer Liches ===
Dalmer liches function the same way regular liches do, most often they are Necromancers (in the medical sense of the term) who make it a hobby to go out of their way and lay the undead to rest. 
Dalmer Lich’s often maintain libraries, and have an ongoing competition to transcribe and master every dalmer word to voice command, and in doing so master wishing technology. Said lich’s are often nothing more than a hand (with jewel phylactery fingers) who work endlessly to scribe every new spell discovered into the organization's Codex, for the purpose of preserving the knowledge. 
=== Vassalich ===
A wizard who, not strong enough to become a lich themselves, swears their soul to an existing lich, who changes them into a lesser form of lich until it deems fit to give them their phylactery so they can go off and complete the metamorphosis.
=== Deilich ===
A lich that is so old that its body has decayed to uselessness, but has such great powers that this doesn't stop it. Nothing is left of a deilich but a skull (or other skeletal part) jammed full of soul gems containing slowly digesting souls. These powerful liches typically manage the incredible feat of warping themselves to the moon, often to gather armies. The process to become a Deilich includes imbedding soul gems to the body as sustenance to avoid the yearly feasting requirement. 
=== Wilitch ===
These are witches brought back by a desire for revenge. Their power is sustained by a pile of flesh that's maintained by killing people, the rest of whom they eat to sustain their existence. They appear normal at first, but their skin turns charcoal black with age, and they can resurrect people into their coven.
=== Warlich ===
A combination of warlock and lich, the concept is that a powerful demon is the phylactery and brings the warlich back to life when it is killed in exchange for its soul. While safer, this makes the lich completely dependent on the demons' good graces for its continued existence. 
=== Death Knights ===
Warlike Lich’s whose phylacteries are their weapons and/or their armor. The trick is that both the weapon and the lich must be destroyed for it to be truly dead. If the armor is worn or the weapon used, it will eventually take possession of the wearer, becoming the lich’s vessel. 
Traditionally, death knights are made by liches from the recently deceased corpses of knights, paladins and other mounted warriors. 
Death knights have two main creation processes. 
Process A: Death Knights are dead bodies that have not and will not decay. The body is controlled by the souls in the blades they wield. The Death Knight's soul is the first one to be sucked into the blade they wield.
Process B: Death Knights made from the corpses of Knights imbued with the souls of warlocks.
== Misc ==
Liches are often confused for Reapers (Demons who can take the life force of one person, convert it to Fountainwater, and give it to another (minus a small fee for itself).
If a kingdom is ruled by the dead, Liches are often in the top hierarchy.
Graveyards are still occasionally called "lichyards"
Soul gems can be considered phylacteries for the Dalmer, as they contain instructions for 3D printing a new body should the original be destroyed. However, the soul gem contains the user's UC at the point of creation, and must be updated manually. Soul gems also have limited range, targets too far from it will suffer from lapses of memory leading up to total memory loss until back in range of the soul gem (generally in a 5km sphere). 
Examples of phylacteries
Needle
Soul gem
Comb
Welt itself (rare)
Satellite (rare)
Familiar
Wand
Egg
Tree
Lich’s own skeleton (by removing every bone surgically, performing the phylactery ritual, then replacing the bone back into the body. Meaning this particular Lich has 206 phylacteries)
Cauldron
Chest
Pyramid
Heart (sometimes causes the heart to become sentient and develop telekinesis)
Vermin (rats, maggots)
Bottle
Ring
Pocket Watch
== Lich kingdoms ==
Liches in some parts of Welt exist to keep the undead in check, but without them the dead roam unchecked. Some try to take the lich's place to rid the world of the undead, such as by sending the undead to their deaths, but the more undead die this way, the more easily they leave the lich's power, in a form of survival instinct and so the problem of keeping them in check persists.