Turn Immunity: Acererak cannot be turned.

Divine corruption. Divine spells and smites targeting acererak count as one level lower. scaling down similarly to upcasting. Additionally Paladin auras are reduced to 5 feet.

magical mastery: Acererak ignore the one spell per turn rule. He also ignore material components

Acererak knows the following spells with a spell save of 23 and a spell attack of +15

Toll the dead, Chill touch, eldritch blast (4 beams+6), lightning lure, 

1st at will: Bane, command, guiding bolt, shield, magic missile

2nd at will, blindness/deafness, hold person, misty step, heat metal, scorching ray

3rd. at will, counterspell, enemies abound, spirit guardians, fireball

4th (4) Banishment, polymorph, psychic lance, sickening radiance

5th (4) cloudkill, steel wind strike, wall of force, cone of cold

6th (4) disintegrate, harm, irresistable dance, scatter

7th (3) delayed blast fireball, finger of death, forecage

8th (3) Antimagic field, feeblemind, maze

9th (2) Time stop, weird

Channel Divinity. (2/day) As an action Acererak may use a channel divinity to either Turn living or use darkness of moil

Turn Living: All living creatures within 100 feey must make a dc 23 Charisma save. If a creature is below 20 health is drops to 0 with 2 failed death saves. Above 20 hp the target is frightened of Acererak and takes 10d6+20 radiant or necrotic damage (whichever is less resisted.) A creature frightened in this manner may repeat the save at the end of it's turn. Ending it on a success.

Darkness of Moil: Magical darkness erupts within 30 feet of you. Each creature within 30 feet must make a dc 23 con save or take 3d10+20 necrotic damage. Half as much on a success.

Multiattack. Acererak makes 3 attacks. He can replace 1 attack with a spell or invoke curse and cannot use grasp of enfeeblement more than once per turn

Grasp of Enfeeblement. The lich’s hand becomes black and emanates little dark flames. Melee Spell Attack: +15 to hit, reach 5 ft., one creature. Hit: 10 (3d6) cold damage. On a hit, the target is chilled and only deals half damage with weapon attacks that use Strength and it has disadvantage on Strength ability checks for 1 minute. At the end of each of its following turns, the target can make a DC 20 Constitution saving throw to remove the chilled effect. Succeeding on the initial save 

Divine ray: +15 to hit. On a hit the target takes 2d12+7 radiant damage. The target must make a dc 20 wisdom save or be charmed by acererak. regarding him as a god. On a success that creature is immune to the secondary effect of this attack. The target may repeat the save at the end of it's turn.

Rotting touch: +15 to hit. On a hit the target takes 4d6+7 necrotic damage and cannot regain hitpoints until the end of it's next turn.

 Invoke Curse. While holding the Staff of the Forgotten One, Acererak expends 1 charge from it and targets one creature he can see within 60 feet of him. The target must succeed on a DC 23 Constitution saving throw or be cursed. Until the curse is ended, the target can’t regain hit points and has vulnerability to necrotic damage. Greater Restoration, remove curse or similar magic ends the curse on the target.

Ignore Metal (Bonus Action) (1/Day). For 1 minute the lich passes through metal harmlessly by magically putting itself slightly out of dimensional phase. It also gains immunity from physical damage caused by metal attacks, but it still takes damage equal to the enchantment bonus of the weapon. For example, a lich using Ignore Metal takes only 2 points of damage when hit by a steel longsword +2. A lich using Ignore Metal can also pass through solid metals as if it where incorporeal.

Corrupt Healing: (3/day) When a creature within 60 feet receives healing Acererak may use his reaction to receive that healing instead. 

4 actions

cast (costs 1) acererak casts an at will spell

Move the sphere. (costs 1) 30 feet straight line. DC 16 dex save. 5d10+10 force damage. only artifacts and legendary items are unharmed.

Distrupt attunement: (Costs 3) Acererak targets one creature within 60 feet. That creature must make a dc 20 charisma save. On a failure they are temporarily unattuned from 1 magic item they are attuned to chosen at random. at the start of the target's turn they can repeat the save.