EQ:lich
Lich is the term given to the necromancer & shadowknight spell series that slowly converts health points into mana, and is the best passive mana regeneration ability in the game. Since lich is a long-term buff that drains health, it can kill a inattentive player if your personal + hp regen and Alternate Ability regen does not fully compensate for the loss.
Lich initially forces the user into a skeletal or spectre form, but necromancers ultimately earn the option to lich without an illusion (one spell provides 2 buffs, one for mana/hp conversion and the other for illusion which can be clicked off).
By it's very nature (+mana regen) lich is a core defining ability of the necromancer class. No form of lich stacks with any enchanter series +mana regeneration buffs.
Lich is not considered a detrimental spell, so does not block Out of Combat Regeneration.