You send a targeted burst of healing energy to accelerate a creatures natural regeneration. When you cast this spell you target one creature within range, they can use their reaction to expend one of their hit dice, they roll the expended die and regain hit points equal to the total rolled plus their Constitution bonus.

The number of hit die the target can expend increases by 1 when you reach 5th level (2), 11th level (3), and 17th level (4) and at 20th level the target can choose to expend any number of hit die.