Inexorable Decay

3rd-level necromancy

Classes: Cleric 3, Sorcerer 3, Warlock 3, Wizard 3

Casting Time: 1 bonus action

Range: 30 feet

Components: V, S

Duration: Concentration, up to 1 minute

An undead creature you can see within range becomes susceptible to necrotic damage. The undead must make a Constitution saving throw or it gains vulnerability to necrotic damage. If the undead possesses resistance to necrotic damage, it loses that resistance for the duration of this spell. If the undead has immunity to necrotic damage, it instead becomes resistant to necrotic damage for the duration of this spell. The creature can attempt a new saving throw at the end of each of its turns to end this effect.