More specifically has there been any lore for a quasi-lich or proto-lich type of monster of lesser strength than a lich or Demi-lich in an officially sanctioned product or from a licensed third party publisher and if so where might I find it?
I'm also aware of a previous question on this subject and my question while more direct might still be considered too vague.
In the event that you are dealing with 5E, I would recommend looking at the Flameskull (MM p. 134).
Blazing green flames and mad, echoing laughter follow a disembodied skull as it patrols its demesne. When the undead flameskull discovers trespassers, it blasts the intruders with fiery rays from its eyes and dreadful spells called up from the dark recesses of its mem9ry. Dark spellcasters fashion flameskulls from the remains of dead wizards. When the ritual is complete, green flames erupt from the skull to complete its ghastly transformation
While it isn't a wizard that has achieved some form of lichdom or un-life, it's unlikely that a wizard potent enough to overcome death would be suited to battle a lower-level character. If you're hell-bent on having them encounter such a creature, I would recommend that you send them against a demilich or a lich that has somehow been weakened, wether it's by having its lair blessed by powerful clerics, or by having part of its phylactery partially destroyed.
I can't find any official source for "quasi-lich." Several unofficial ones, but nothing official.
There HAS been a "demi-lich," first described I think in the old 1st edition AD&D module "Tomb of Horrors." It was not something you'd want a group of 4th level character to meet.
