Archnecromancer

Necrotic Resistance. The Archnecromancer has advantage on saving throws against spells and weapons that deal necrotic damage.

Spellcasting. The Archnecromancer is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). The necromancer  can cast  invisibility on itself at will and has the following wizard spells prepared:

Cantrips (at will): chill touch, spare the dying

1st level (4 slots): false life, mage armor (self), inflict wounds

2nd level (3 slots): blindness/deafness, gentle repose, ray of enfeeblement

3rd level (3 slots): animate dead, bestow curse, revivify,speak with dead, vampiric touch

4th level (3 slots): banishment, fire shield, stoneskin counterspell

5th level (3 slots): blight

6th level (1 slot): circle of death, create undead, eyebite,harm, magic jar 

7th level (1 slot): symbol, finger of death, resurrection

8th level (1 slot): clone

9th level (1 slot): astral projection, true resurrection

Shortsword of Life Stealing. 3 (1d6)piercing damage. When you attack a creature with this magic weapon and roll a 20 on the attack roll, that target takes an extra 10 necrotic damage if it isn't a construct or an undead. You also gain 10 temporary hit points.

Shortsword of Wounding. 3 (1d6)piercing damage. Once per turn, when you hit a creature with an attack using this magic weapon, you can wound the target. At the start of each of the wounded creature's turns, it takes 1d4 necrotic damage for each time you've wounded it, and it can then make a DC 15 Constitution saving throw, ending the effect of all such wounds on itself on a success. Alternatively, the wounded creature, or a creature within 5 feet of it, can use an action to make a DC 15 Wisdom (Medicine) check, ending the effect of such wounds on it on a success.

Withering Touch. Melee Spell Attack: +7 to hit, reach 5 ft., one creature. Hit: 5 (2d4) necrotic damage.