Undying Cultist Summoner

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 summoner's attacks count as magical for the purpose of overcoming resistance
Otherworldly Pact The cultist summoner's spells are automatically cast at its highest available spell slot. Supernatural Devotion The cultist summoner has advantage on saving throws against being charmed or frightened
Supernatural Aid The cultist summoner cannot lose concentration on a spell effect to summon a creature by taking damage.
Summoner's Vengeance (1/long rest) When the cultist summoner is reduced to 0 hitpoints, a CR 3 creature (either an Aberration, Celestial, Draconic, Elemental, Fey, Fiend, Undead or other creature appropriate for the cultist) appears in the nearest unoccupied space. This creature lasts for 1 minute and is considered an ally to the cultist and its allies and acts on the cultist's initiative.

Spellcasting
The cultist summoner is an 8th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +7 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 (2 slots) Ray of Enfeeblement
3rd Level Spells(3 slots) Hex, Spiritual Guardians, Find
Familiar, Guardian of Faith, Animate Dead, Vampiric Touch, Summon Undead

Eldritch Blast. Ranged Spell Attack: +7 to hit, 150ft., one
target. Hit: 10 (1d10+4) 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
summoner can recover all expended spell slots

Call from the Beyond(Recharge 5-6) The cultist
summoner can summon a CR 3 creature (either an
Aberration, Celestial, Draconic, Elemental, Fey, Fiend,
Undead or other creature appropriate for the cultist)
appears in an unoccupied space within 30ft. This
creature lasts for one hour, until it is dismissed, if it is
reduced to 0 hitpoints, or if the cultist summoner uses
this ability again. This creature is considered an ally to
the cultist and its allies and acts on the cultist's
initiative

Deathly Blast When the cultist uses Eldritch Blast, the
target cannot regain hitpoints until the end of its next
turn..

Summoner's Fury The cultist summoner can use its
bonus action to command a creature summoned by it
to move up to half its movement speed and make an
make a single attack against a creature of the cultist
summoner's choice within range.

Summoner's Fury When the cultist summoner takes damage, it can use its reaction to command a creature summoned by it to make a weapon attack against the attacker if it is in range.

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.