Call of the Void

You call to a creature within range and begin the incantations for an insidious bargain. Until the spell ends, both the caster and the target bust make a Wisdom saving throw at the start of each of their turns. This first person to fail against this spell three times suffers 10d10 necrotic damage, the other creature regains hit points equal to half the amount of necrotic damage dealt and the spell ends.

If the spell ends before the caster or target has failed three times, the spell ends with no effect. If both of you fail on the same turn, the caster wins. 

Credit to Sarsen Games and their Magnus Tome of Unshackled Spells