Balance of Life

You choose 2 creatures within range:  One to give, and one to receive.  A ghostly green beam of light connects the 3 of you.  The giver feels the chill of the grave as their life essence is drained from them; a portent of death to come as they recieve Necrotic damage equal to the spell casters hit die type.  You, as the conduit between the two lose 1 hit die slot  until your next long rest.  The receiver feels a rush of heat and comfort as they recieve healing equal to two times the spell caster's hit die type. This brings the transaction balance to zero as there is no such thing as free.

*Casting at a higher spell level increases the damage by 1 hit die, the healing by 2 hit die, and loss of one extra hit die slot per level above 1.

** If the opponent passes its CON Save, they take no damage.  However, the hit die spent for the spell from the caster still heals the intended recipient.