Ritual of Lichdom
The Ritual of Lichdom is a profane, vile process. One which quite literally rips the mortal soul's connection to the caster's living body. As such, the process is one which only undertaken by the most truly evil of mages. Furthermore, the ritual is not shared knowledge.
What is required are a phylactery and an unbinding potion. The unbinding potion is a rigorous process requiring unwavering dedication and patience.
Unbinding Potion In order to complete the multi-step rites, the caster must imbibe a potion so vile that it doesn't transform the body--it shatters the soul, ejecting it violently from the body. It doesn't kill, rather it causes complete and total metaphysical rejection.
The ingredients for the unbinding potion are as follows and must be carried out in the correct order. First, the caster must collect ashes of despair. This ingredient is made by immolating a living person who was tortured to the edge of psychological break. The caster must mix these ashes of despair with mandrake root, belladonna, and the blood of a (slaughtered) unicorn. All to be filtered over and/or through a stillborn heart, brought to a rolling boil over a candle made from the tongue of a cleric/priest.
Once the first draught is complete, the caster must imbibe this vile mixture within seven days lest the ingredients become inert. Once consumed, the caster must within 24 hours conceive a child with a willing participant.
The child born under these circumstances must then be fed a drink made of the blood of the caster and the tears of its mother, after suffering betrayal and a broken heart.
Finally, the caster must perform and prepare the ritual to bind his/her soul to the prepared phylactery. During the ceremony, the child born of the caster must be sacrificed and their blood consumed by the mage who seeks to become a lich. If everything was performed correctly, the transformation into lichdom will be complete. If however, the caster fails to perform each part of this process correctly, they will instead fall dead on the spot - resurrection magic cannot and will not work on them from this point forward.