Cult Leader of Undeath

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.

Otherworldly Favor Once on each of its turns, the cultist
leader can add a d8 to an attack roll, ability check,
saving throw, or damage roll of its choice.
Magical Attacks The cult leader's attacks count as
magical for the purpose of overcoming resistance.
Magical Resistance The cult leader has advantage on
saving throws against spells and magical effects.
Legendary Action(3/day) Upon failing a saving throw, the
cult leader can choose to succeed. Upon using this
feature, it regains one expended spell slot.
Otherworldly Pact The cult leader's spells are
automatically cast at its highest available spell slot.
Supernatural Devotion The cult leader has advantage on
saving throws against being charmed or frightened.

Spellcasting
The cult leader is an 20th-level spellcaster. Its
spellcasting ability is Charisma (spell save DC 19, +11
to hit with spell attacks).

Cantrips Toll the Dead Eldritch Blast(see below), Thaumaturgy,Guidance
1st Level Spells (4 slots) Inflict Wounds
2nd Level Spells (4 slots) Ray of Enfeeblement
3rd Level Spells(4 slots) Animate Dead, Vampiric Touch, Summon Undead
4th Level Spells (4 slots) Blight
5th Level Spells(5 slots) Hex, Planar Binding,Counterspell, Dispel Magic,Dimension Door, Spirit GuardiansAntilife Shell, Negative Energy Flood Mystic Arcanaum Otherworldly Form, Create Undead,Finger of Death, Circle of Death.

Mystic Arcanaum Otherworldly Form, Create Undead,Finger of Death, Circle of Death

Multiattack The cult leader can cast make three attacks
with its Pact Blade
Pact Blade. Ranged Spell Attack: +11 to hit, 5ft., one
target. Hit: 12 (1d10+6) slashing damage + 9(2d8)
force damage.
Eldritch Blast. Ranged Spell Attack: +11 to hit, 300ft.,
one target. Hit: 12 (1d10+6) force damage. This attack
hits four times against the same or separate targets.
This attack is considered to be a cantrip
Patron's Bestowal (Recharge 5-6)
When available, the cultist had can use one of the
following abilities as an action
Devotion's Favor(Recharge 5-6) The cult leader can
recover all expended spell slots
Mystic Arcanaum(Recharge 5-6) The cultist leader can
cast a spell of its choice from its Mystic Arcanaum at
9th level from their patron class list without expending
a spell slot.

Deathly Blast When the cultist uses Eldritch Blast, the
target cannot regain hitpoints until the end of its next
turn..
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..
Patron Bestowal Option: Death's Touch(Recharge 5-6)
One creature of the cultist's choice must succeed a
Constitution saving throw equal to the cultist's spell
save DC.
On a failed saving throw, the target takes necrotic
damage equal to a number of d8s equal to twice the
cultist's proficiency bonus and its hitpoint maximum is
reduced by the damage taken. On a successful saving
throw, creatures take half damage and are otherwise
unaffected.
If this attack reduces a creature to 0 hitpoints, the
target instantly dies and returns to life as a zombie
under the control of the cultist.
A creatures hitpoint maximum returns to normal after a
long rest.

Divine Command The cult leader can use its bonus
action to command one of its allies within range to use
its reaction to move up to half its movement speed and
to make an attack against a creature within range.
Eldritch Storm(Recharge 5-6) The cult leader can use its
bonus action use its Eldritch Blast attack. 

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. 

(3/turn)
Command Cultist(1 actions) The cult leader can
command an ally that it can see within range to make
an attack against a creature that they can see in range
using its reaction
Movement(2 actions) The cult leader can move up to its
movement speed without provoking attacks of
opportunity
Spell(2 actions) The cult leader can cast a spell of 5th
level or lower
Patron's Resilience(3 actions) The cult leader can end a
status condition or spell effect on themself as an attack.