The Secret to Lichdom

One of the 9 book of The Mouthless One which holds the Secret to Lichdom

• Craft a phylactery and imbue it with the power to contain the beneficiary's soul
• Concoct a potion of transformation that turns the beneficiary into a lich

Construction of the phylactery takes 10 days. Concocting the potion takes 3 days. The two items can't be crafted concurrently.

Drinking the potion tries to sever the soul from the body, and can result in perminate death of body is not strong enough.  The soul lingers in the ethereal plane close to the lich until it is sealed in a phylactery.
The creature immediately becomes undead, and gain unusual nature, as well as other attributes of a Lich.
The phylactery requires the Magic Jar spell to be cast to complete the ritual.

The Phylactery

The phylactery cost 1,500gp per level of the character. Phylactery preparation is similar to the Imprisonment Spell. The phylactery must be a non magical inorganic container of high quality craftsmanship. A phylactery is traditionally an amulet in the shape of a small box, but it can take the form of any item possessing an interior space into which arcane sigils of naming, binding, immortality, and dark magic are scribed in silver. In older editions the most common form of a phylactery would be that of a sealed metal box containing strips of parchment bearing magical phrases. The phylactery can exist in other forms as well, though it must either contain or bear the arcane inscriptions used to bind the soul forevermore.
The phylactery is resilient beyond measure and nigh impervious to destruction. Destroying a phylactery is no easy task and during the process of crafting you must specify a specific condition such as a ritual, item, or weapon that can bring about it’s destruction. An example from Waterdeep: Dungeon of the Mad Mage details that it is possible to learn of a phylacteries destruction by casting Legend Lore on the phylactery, “Destroying the lich's phylactery requires that it be struck by eight disintegrate spells at the same time. A legend lore spell cast on the box provides the following insight: "Seek out eight magi who possess the power of disintegration and bring them to common purpose. Their combined force can destroy the phylactery." Other reliable divination spells provide similar advice.” . It may very well be possible for someone to learn of the process to become a lich from a plethora of Legend Lore castings on a phylactery. Phylactery Examples from the Libris Mortis:
Sample Phylacteries

1. A hollow silver sphere hanging from a silver chain and containing strips of inscribed parchment
2. A gold ring bearing arcane inscriptions on the inside of the band
3. A hollow gold sphere containing strips of inscribed parchment, set atop a darkwood staff
4. An ivory box bearing arcane sigils across all six sides
5. A sealed clay jar containing strips of inscribed parchment
6. A crystal cube with magical phrases carved on all six sides
7. A hollow platinum circlet containing tiny strips of inscribed parchment rolled tightly inside
8. A gold-plated skull with magical phrases engraved upon the teeth
9. An iron flask containing strips of inscribed parchment
10. A flawless diamond bearing tiny magical inscriptions, set into a golden crown

Potion of Xhecu

• Arsenic (2 drops of the purest distillate)
• Belladonna (1 drop of the purest distillate)
• Blood (1 quart of blood from a dead unicorn yearling or dead pegasus foal, killed by wyvern venom)
• Blood (1 quart from a dead humanoid slain by a phase spider
• Blood (1 quart from a vampire or vampire spawn)
• Heart (the intact heart of a humanoid killed by poisoning, a mixture of arsenic and belladonna must be used)
• Reproductive glands (from seven giant moths, dead for less than 10 days, ground together)
• Venom (1 pint or more, drawn from a phase spider less than 30 days prior)
• Venom (1 pint or more, drawn from a wyvern less than 60 days prior)

The potion must be consumed under the light of a full moon and the soul of the person who’s heart is used in the potion is sacrificed to the phylactery either upon creation of the phylactery or before consuming the potion of transformation.
Possible Archlich/Good Lich Altered Ingredients

• Tears of a Celestial (#3)
• Blood of a Dragon or some other powerful magical being (#4)
• Anointment of the phylactery in the caster’s blood replaces ingredient (#6)