Arkunuk

Innate Spellcasting. The warlock’s innate spellcasting ability is Charisma. It can innately cast the following spells (spell save DC 18), requiring no material components:

At will: alter self, false life, levitate shield, silent image

2/day each: feeblemind, finger of death, plane shift

Spellcasting. Arkunuk spellcasting ability is Charisma (spell save DC 18, +9 to hit with spell attacks). Arkunuk has following Warlock spells prepared:
Cantrips (at will): chill touch, eldritch blast, fire bolt, friends, mage hand, minor illusion, prestidigitation, shocking grasp

1st–7th level (6 7th-level slots): banishment, burning hands, crown of stars, etherealness, flame strike, hellish rebuke, magic circle, mental prison, scorching ray, scrying, stinking cloud, suggestion, wall of fire

Staff of the Forgotten One.

Invoke Curse. The Staff of the Forgotten One has 7 charges and regains 1d4 + 3 expended charges daily at dawn. While holding the staff, you can use an action to expend 1 charge and target one creature you can see within 60 feet of you. The target must succeed on a Constitution saving throw (using your spell save DC) or be cursed. While cursed in this way, the target can’t regain hit points and has vulnerability to necrotic damage. A greater restoration, remove curse, or similar spell ends the curse on the target.

Destroying the Staff. A creature in possession of the staff can use an action to break it over one knee or a solid surface. The staff is destroyed and releases its remaining magic in an explosion that expands to fill a 30-foot-radius sphere centered on it. Each creature in the area must make a DC 18 Dexterity saving throw, taking 132 (24d10) force damage on a failed save, or half as much damage on a successful one. When the staff is destroyed, the life force of the Forgotten One is released to the afterlife. Where it goes is anyone’s guess.

Staff of the Forgotten One. Melee Weapon Attack:+7 to hit, reach 5 ft., one target. Hit: 11 (3d6 + 3) necrotic damage.