Wilting Smite (GH)

As part of casting this spell, you must expend two hit dice or the spell automatically fails. If you do, the next time you hit a creature with a melee weapon attack during this spell’s duration, blood flows over your weapon then desiccates into black spores falling onto the attack’s target, and the attack deals an extra necrotic damage to the target. Roll the hit dice expended to cast this spell, and the total equals the amount of this extra necrotic damage. Additionally, the creature loses all damage resistances it has until the start of your next turn.

From Ghostfire Gaming's Grim Hollow