Undead Fortitude. If damage reduces the cursed cleric to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the cursed cleric drops to 1 hit point instead.

Turn Undead Immunity. The cursed cleric is immune to effects that turn undead. It only alerts it to the caster! 

Chain Attack. Melee Weapon Attack: Chain and hook +3 to hit, reach 10 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage plus (1d8 + 1) Cold Radiant damage. 

Targets must make DC 15 Dexterity saving throw or be grappled by the chain and hook. The chains icy touch burns unnaturally, the pain felt even through armour. For each round a target is grappled they will take (1d8 + 1) Cold Radiant damage. 

Seraphic Drain. Once per turn as a bonus action, if the cursed cleric is successfully grappling an opponent, the cursed cleric may use this ability to steal the soul of it's grappled target. Thrusting it's skeletal head into the opponents face, a blue tinged mist will painfully be pulled from the target and into the eye sockets, nose, and mouth of the cursed cleric and thus inflicting on the target (1d12) Radiant damage.

This attack will continue as long as the grapple is unbroken. Opponents who break the grapple on their next turn cannot be attacked in this way again, unless the cursed cleric again successfully grapples them. 

Should the target be killed in combat with the cursed cleric (regardless of damage or actions of others that contribute to the target's death), and it's target is a holy person such as a cleric, who took damage from at least three Seraphic Drain attacks, over any three rounds or turns, the cursed cleric has successfully stolen the target's soul! The cursed cleric begins the next round with the target's soul as it's own, gaining all the spells and clerical abilities of the dead opponent, except for any spells or abilities that inherently do good (such as healing). The cursed cleric also starts this round at it's full hit points.

As long as the soul is in the cursed cleric's possession, the killed opponent cannot be resurrected or raised in any way (even with a Wish). Should the cursed cleric be killed or destroyed, the soul is set free and thus may return to it's rightful body by magical or other mystical ways. 

Non-holy beings do not loose their soul to the cursed cleric in this attack, though they find stray dark and terrible thoughts plague them for some days. Should they be killed in this way it is unknown what happens to the soul, though it is known the cursed cleric cannot steal it.