You can corrupt your healing spells with necrotic energy. You gain the following benefits:

• When you cast a spell that causes a creature to regain hit points, you can choose to cast an accursed version of that spell. The target of the spell must make a Constitution saving throw against your spell save DC, or take necrotic damage equal to the number roll on the spell die on a failed save or half as much on a successful one. The spell must require a dice roll to be affected by this feat.
• When you cast an accursed healing spell, you can choose to either cause damage or restore hit points to undeads. If the spell affects an area, you can make this choice individually for each undead in the area.
• Your healing spells restore a number of additional hit points equal to your spellcasting ability when used on undead creatures.