Cultist Executioner

Vampire's Sight The cultist's vision is not obscured
by magical darkness.
Death Magic Whenever the cultist deals force
damage, it deals necrotic damage instead

Undying Gift Whenever the cultist is reduced to 0
hitpoints, it can make a Charisma saving throw with a
DC equal to half the damage dealt (minimum 10). It
cannot benefit from this feature if tis takes radiant
damage or if it is hit with a critical hit. On a successful
saving throw, it regains 1 hitpoint instead.

Magical Attacks The cultist executioner's attacks count
as magical for the purpose of overcoming resistance
Otherworldly Pact The cultist executioner's spells are
automatically cast at its highest available spell slot
Supernatural Devotion The cultist executioner has
advantage on saving throws against being charmed or
frightened
Zealous Empowerment When the cultist executioner
deals a critical hit, they can triple the damage die
instead of doubling it.

Zealous Blessing (Recharge 5-6) At the start of each of
its turns, the cultist executioner can add an additional
damage die to its Pact Blade or Eldritch Blast until the
end of its next turn.

Spellcasting
The cultist executioner is an 6th-level spellcaster. Its
spellcasting ability is Charisma (spell save DC 13, +5 to
hit with spell attacks).

Cantrips Toll the Dead Eldritch Blast(see below), Thaumaturgy, Guidance
1st Level Spells (1 slots) Inflict Wounds
2nd Level Spells (1 slots) Ray of Enfeeblement
3rd Level Spells(2 slots) Hex, Spirit Shroud, Spiritual Weapon, Animate Dead, Vampiric Touch, Summon Undead

Multiattack The cultist executioner can make two
attacks with its Pact Blade
Pact Blade. Melee Weapon Attack: +5 to hit, 5ft., one
target. Hit: 5 (1d10+3) slashing damage
Eldritch Blast. Ranged Spell Attack: +5 to hit, 150ft., one
target. Hit: 8 (1d10+3) force damage. This attack hits
twice against the same or separate targets. This attack
is considered to be a cantrip
Devotion's Favor(1/short or long rest) The cultist
executioner can recover all expended spell slots

Deathly Pact Blade When the cultist makes an attack
with its Pact Blade, the target cannot regain hitpoints
until the end of its next turn..

Zealous Mark One creature the cultist executioner can
see within 30ft is marked for death. Until the cultist
executioner uses this ability again on another creature,
it can make an additional attack with its Pact Blade or
Eldritch Blast whenever it takes the Attack action

Death's Lash When the cultist takes damage from an
attacker within 60ft. of it, the attacker must succeed a
Constitution saving throw against the cultist's spell
save DC. On a failed saving throw, it takes necrotic
damage equal to the damage taken and the target's
hitpoint maximum is reduced by that amount as well. If
a creature is reduced to 0 hitpoints, it instantly dies. A
creature's hitpoint maximum can be restored by taking
a long rest.

The dead creature turns into a undead provided the body is not destroyed.