The Lich Ritual

You cannot take this spell through level-up and can only be obtained by copying it from a liches spell book or from contact with Vecna the lich-god anyone attempting to cast this spell other than a Necromancer wizard will have die without the resurrection effect.

You create a ritual circle comprised of one-hundred candles around you before chanting the ritual of lichdom for four days, the humanoids soul will then be harvested to transform the trinket or gemstone into a phylactery. then you drink the poison in the goblet and die.  After one week there is a fifty-percent chance +10% per point of constitution bonus that you possess that you will be resurrected as a lich.  If you are not resurrected your body will instead erupt into fifty shadows which must be killed before you can move onto the afterlife or be resurrected. This spell cannot be dispelled once cast even by means of a wish spell.

If you are successfully resurrected you will gain the following benefits:

Paralyzing Touch -  As an action you may use Paralyzing Touch making a melee spell attack reach 5ft. dealing 3d6 cold damage then the target must make a Con. save against your spell save DC  or be paralyzed for 1 minute being allowed to repeat the savingthrow at the end of each of it's turn ending the effect on itself if it succeeds.

Cold Unlife -  You have resistance to cold and necrotic damage. You are also immune to disease.

One of them - undead with an intelligence of six or lower will ignore believing you are one of them, you are undead in addition to your other creature types.

Lord of The Dread Horde - undead you control deal an additional amount of damage equal to you intelligence modifier minimum of 1.  Zombies you control have their speed doubled skeletons you control gain advantage against on attacks and to track enemies below half heath.  When you cast a spell that reanimates the dead you may cast it one level higher than the spellslot expeneded.

Eternal - you do not suffer adverse effects of aging and cannot die of it. If your phylactery has not been destroyed when you die you will gain a new lich body in 1d10 days that appears within 5 feet of the phylactery.  Your phylactery must be fed a soul every ten days in order to keep working if this not done you will slowly decay over the course over twelve days taking a level of exhaustion every 2 days until eventually succumbing to death.  You also do not need to eat, sleep or breathe.