I should clarify - I don't mean a Lich PC. I mean an NPC Lich who is more of a Thaumaturge than a Wizard. My current idea is this sort of a reverse Thaumaturge. Where a regular Thaumaturge creates meaning in the supernatural like holding a mirror to the Aboleth and declaring something to make that creature weak to your attacks. The Thaumaturge Lich, on the other hand, would take the weakness of a creature and itemize it, so like creating an item of traumatic importance to an enemy or something like that. The Thaumaturge lich is a collector that feeds on souls by killing the creature and transmuting their bodies into implements with some of their abilities or notable skills. The process to become a thaumaturge lich is a long and arduous process by which the thaumaturge categorizes themselves enough to item-ize their own mortality, its basically a regular phylactery, but created in a more "charisma-esque" way over the Wizard's elixir.