In a recent issue of Suicide Squad Enchantress made the Squad undead so that they couldn't be detected by a robot. I thought this was pretty cool and would be a fun Continual Light/Light City spell. The following spells are usable by Magic-Users and Necromancers.
3rd level -
Become the Unliving - Range: Touch; Duration: permanent. The target must make a saving throw. If they fail they become an undead creature. They may voluntarily fail the saving throw. They may be turned as an undead creature of their hit dice. They no longer heal naturally and magical healing no longer works. However, they regain 1d3 HP from every point of flesh they consume.
4th level -
Return to Life - Range: Touch; Duration: Permanent. Target undead creature must make a saving throw. If they fail their flesh regrows, mends, and they become living once again. They may voluntarily fail this saving throw.