Necrotic Infusion 
Feat 4ClericConcentrateMetamagicSource Core Rulebook pg. 123 1.1Prerequisites harmful font, evil alignment
You pour negative energy into your undead subject to empower its attacks. If the next action you use is to cast
harm to restore Hit Points to a single undead creature, the target then deals an additional 1d6 negative damage with its melee weapons and unarmed attacks until the end of its next turn. If the
harm spell is at least 5th level, this damage increases to 2d6, and if the
harm spell is at least 8th level, the damage increases to 3d6.
Traits
Concentrate: An action with this trait requires a degree of mental concentration and discipline.
Metamagic: Actions with the metamagic trait, usually from metamagic feats, tweak the properties of your spells. You must use a metamagic action directly before Casting the Spell you want to alter. If you use any action (including free actions and reactions) other than Cast a Spell directly after, you waste the benefits of the metamagic action. Any additional effects added by a metamagic action are part of the spell’s effect, not of the metamagic action itself.