Akar Kessel

Sunlight Sensitivity:  While in sunlight, Kessel has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight 

Spellcasting. Kessel is a 5th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). Kessel has following Necromancy spells prepared:
Cantrips (at will): Chill Touch, Ray of Frost, Toll the Dead, Mind Sliver
1st level (4 slots): Catapult, Ice Knife, Ray of Sickness, Shield

2nd level (3 slots): Locate Object, Misty Step, Rime's Binding Ice

3rd level (3 slots): Animate Dead, Counterspell, Glyph of Warding, Vampiric Touch

4th level (3 slots): Evard's Black Tentacles, Ice Storm, Summon Greater Demon

5th level (1 slot): Mislead

Staff of Withering:  The staff can be wielded as a magic quarterstaff. On a hit, it deals damage as a normal quarterstaff, and you can expend 1 charge to deal an extra 2d10 necrotic damage to the target. In addition, the target must succeed on a DC 15 Constitution saving throw or have disadvantage for 1 hour on any ability check or saving throw that uses Strength or Constitution. 3 charges/day regain 1d3 charges per next dawn.

Multiattack: The wight makes two quarterstaff attacks. It can use its Life Drain in place of one quarterstaff attack.

Quarterstaff: Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 5 (1d6+ 2) bludgeoning damage.

Life Drain: Melee Weapon Attack: +8 to hit, reach 5ft, 1 target. Hit: 5 (1d6+2) necrotic damage. The target must succeed on a DC 13 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

A humanoid slain by this attack rises 24 hours later as a zombie under the wight's control, unless the humanoid is restored to life or its body is destroyed. The wight can have no more than twelve zombies under its control at one time.