Death Void

As a spell that only the master warlocks know and can safely use. Anyone creature within a 15 ft radius must roll a wisdom saving throw of 10 or higher or lose their soul to the caster. If they don't succeed then they will be under the control of the caster with half the usual health until death. They can't be healed by normal means but instead if someone uses a necromancy spell within a 30 ft radius of them.