Supernatural Resistance.  Zadius has resistance to bludgeoning, piercing, and slashing damage from nonmagical weapons.

Dark Devotion: Zadius has advantage on saving throws against being charmed or frightened.

Spellcasting. Zadius Mortem is a 17-level spellcaster. His spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). Zadius has the following spells prepared:
Cantrips (at will): Eldritch Blast, Mage Hand.

1st level (6 slots): Hellish Rebuke, Inflict Wounds.

2nd level (6 Slots): Crown Of Madness, darkness.

3rd Level (5 Slots):Animate Dead, Bestow Curse.

4th Level (5 Slots): Greater Invisibility, Confusion.

5th Level (4 Slots): Mislead, Dominate Person.

6th Level (4 Slots): Harm, Heal.

7th Level (3 Slots): Resurrection, Teleport.

8th Level (3 Slots): Incendiary Cloud, Power Word Stun.

9th Level (2 Slots): Time Stop, Power Word Kill.

MultiAttack. Zadius makes 1 attack with their Scimitar and one other action.

+3 Scimitar. Melee Weapon Attack: +10 to hit, reach 5 ft., one creature. Hit: 10 (1d12 + 5 slashing damage.

Lay On Hands. Zadius has 50 points in your pool this replenishes after you take a long rest. As a Bonus Action, you can touch a creature (which could be yourself) and draw power from the pool of healing to restore a number of Hit Points to that creature, up to the maximum amount remaining in the pool.

Zadius can also expend 5 Hit Points from the pool of healing power to remove the Poisoned condition from the creature; those points don’t also restore Hit Points to the creature.

Dread Counterspell. Zadius utters a dread word to interrupt a creature they can see that is casting a spell. If the spell is 3rd level or lower the caster must succeed a constitution saving throw (DC 19)  or it fails and has no effect. If the spell is 4th level or higher, Villain makes an Intelligence check (DC 13 + the spell's level). On a success, the spell fails and has no effect.