Wither & Bloom (CoS)

When the spell is cast, you can target as many creatures as you'd like within a 10-foot radius to make a Constitution saving throw. Any that fail the save takes 2d6 necrotic damage. Then, you can choose one creature within that initial radius that is able to roll an unspent hit dice (if they have one) and regain hit points equal to the result plus your spellcasting modifier. 

When the spell is upcast, the necrotic damage and the number of Hit Dice that can be spent increase by one per spell slot above 2nd level. It's important to note that a creature must have at least one unspent Hit Dice to be targeted by the healing effect.