Acererak Setup

[glasseskid93]

I found Acererak's spell compliment is somewhat... off. Arcane lock and knock? Really? A multidimensional Lich capable of capturing and creating Gods has those spells prepared when he travels through the Abyss and Nine Hells to catch servants? And not wish?! I know wish can be pretty nasty, as it tanks your strength score and gives you some gnarly sicknesses, but we're talking about Acererak here. That in mind, I took some liberties with the spell prepped and his combat tactics, gave him some fancy new kicks and wanted some input on it:

Spoiler: PLAYERS BEWARE!

Show

Acererak
Medium undead, neutral evil
Armour Class 21 (natural armour)
Hit Points 285 (20d8+60)
Speed 30 ft., fly 30 ft.

Str 13 (+1) Dex 16 (+3) Con 20 (+5) Int 27 (+8) Wis 21 (+5) Cha 20 (+5)

Saving Throws Con +12, Int +15, Wis +12
Skills Arcana +22, History +22, Insight +12, Perception +12, Religion +15
Damage Resistances cold, lightning
Damage Immunities necrotic, poison, psychic (from mind blank); bludgeoning, piercing, and slashing damage from nonmagical attacks
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, paralyzed, petrified, poisoned, stunned
Other Immunities emotion and thought detection, divination spells (from mind blank)
Senses truesight 120 ft., passive Perception 22
Languages Abyssal, Common, Draconic, Dwarvish, Elvish, Giant, Infernal, Old Tongue, Primordial, Undercommon
Challenge 23 (50,000 XP)

Special Equipment. Acererak carries the Staff of the Forgotten One (with 5 charges). He wears winged boots and a talisman of the sphere with a sphere of annihilation.
Legendary Resistance (3/Day). If Acererak fails a saving throw, he can choose to succeed it instead.
Rejuvination. When Acererak is destroyed, he will gain a new body in 1d10 days, provided he has a phylactery, regaining all his hit points and becoming active again. The new body appears within 5 feet of the phylactery, the location of which is hidden.
Spellcasting. Acererak is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 23, +15 to hit with spell attacks). Acererak has the following wizard spells prepared:
Cantrips (at-will): chill touch, mage hand, toll the dead
1st-level (at-will): comprehend languages, identify, magic missile, shield
2nd-level (at-will): blindness/deafness, detect thoughts (c)
3rd-level (at-will): counterspell, dispel magic, lightning bolt, speak with dead
4th-level (3 slots): blight, greater invisibility (c)
5th-level (3 slots): legend lore, synaptic static
6th-level (3 slots): disintegrate, soul cage
7th-level (3 slots): finger of death, force cage, teleport, plane shift, power word pain
8th-level (2 slot): feeblemind, mind shield*
9th-level (2 slot): foresight*, wish
* Cast before combat
Turn Resistance. Acererak has advantage on saving throws against any effects that turns undead.

Actions
Paralyzing Touch. Melee Spell Attack: +12 to hit, reach 5 ft., one creature. Hit: 10 (3d6) cold damage, and the target must succeed a DC 20 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on a success. This attack’s spellcasting ability is Charisma. (I saw that it was a spell attack that used strength to hit, so after taking a look at his stats I decided to use charisma as the "spellcasting ability". It was between that and constitution, so I'm open to thoughts.)
Staff (+3 Quarterstaff). Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 7 (1d6+4) bludgeoning damage plus 10 (3d6) necrotic damage, or 8 (1d8+4) bludgeoning damage plus 10 (3d6) necrotic damage when used in two hands.
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 a DC 23 saving throw or be cursed. Until the curse is removed. The target can’t regain hit points and has vulnerability to necrotic damage. Greater restoration, remove curse, or similar spell ends the curse on the target.

Legendary Actions
Acererak can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. Acererak regains spent legendary actions at the start of his turn.
At-Will Spell. Acererak casts one of his at-will spells.
Melee Attack. Acererak uses Paralyzing Touch or makes one melee attack with his staff.
Frightening Gaze (Costs 2 Actions). Acererak fixes his gaze on one creature he can see within 10 feet of him. The target must succeed a DC 20 Wisdom saving throw or become frightened for 1 minute. The target can repeat this saving throw at the end of each of its turns, ending the effect on itself on a success. If the target’s saving throw is successful or the effect ends for it, the target is immune to Acererak’s gaze for 24 hours.
Talisman of the Sphere (Costs 2 Actions). Acererak uses his talisman of the sphere to move the sphere of annihilation under his control up to 90 feet.
Disrupt Life (Costs 3 Actions). Each creature within 20 feet of Acererak must make a DC 20 Constitution saving throw, taking 42 (12d6) necrotic damage on a failed save, or half as much on a successful one.

Tactics
Before Combat. Acererak casts foresight and mind blank at the beginning of each day to ensure he is prepared for all threats before him.
During Combat. Acererak opens by activating his winged boots and casting greater invisibility to analyze the enemy force. On subsequent turns, he moves randomly through the battlefield to maintain confusion while using his talisman of the sphere and sphere of annihilation to harass the enemies. After identifying the arcane caster, he moves to an advantageous position and casts feeblemind on the caster. Should the caster save, he casts power word pain on his next turn, attempting to incapacitate the arcane caster first.
Now visible, he maintains an advantageous position as best he can and casts forcecage in the box format, attempting to capture any further casters in the party. He shifts to debilitating further party members using the curse effect from his Staff of the Forgotten One. He then begins harassing the group further, using spells as necessary to eliminate as many threats as possible, such as targeting fighters with lightning bolt and rogues with blindness/deafness.
Should an enemy die and his reaction be available, Acererak will cast soul cage to maintain the advantage over the party, generally using it to keep his hit points as high as possible. Otherwise, he will use his reaction to cast counterspell, but never above 3rd-level, as he is confident that he will be powerful enough to dispel any magic the mortals could cast.

I rolled for the current charges in the Staff. My party's heading into the final room on Tuesday, and the current setup is a shadow monk/champion fighter, death domain cleric, war wizard, storm domain cleric, and path of ancients paladin.

[Unoriginal]

Arcane Lock and Knock make sense when you include the fact that Acererak's main and most beloved way of both phylactery-feeding and entertainment is creating or taking over dungeons and making them as sadistic as he can.

As for Wish, assuming he even knows the spell, he might simply not have prepared it for what was for him a casual day.

[Asmotherion]

Arcane Lock and Knock make sense when you include the fact that Acererak's main and most beloved way of both phylactery-feeding and entertainment is creating or taking over dungeons and making them as sadistic as he can.

As for Wish, assuming he even knows the spell, he might simply not have prepared it for what was for him a casual day.

it's safe to assume he knows it considering his past accomplishments.

On the other hand a Final Battle against a Wish user is pretty much encouraging the DM to come up with some unfair bullsh1t to Tpk the PCs.

if you feel more comfortable you can fluff it that he used it so many times for things "other than duplicating a spell" he cannot use it ever again. Seems legit on this particular character. And that's how Wish functions.

[Unoriginal]

it's safe to assume he knows it considering his past accomplishments.

Possible, but he seems the kind to search for mighty rituals to do the job, instead. Acererak isn't afraid of waiting to accomplish his goals, and I don't see him keen to rely on something that could backfire like Wish.

[OvisCaedo]

Even avoiding the backfiring effects, "any 8th or lower spell as a standard action" is a pretty potent thing to pass up. Especially for a ridiculous creature that has TWO ninth level spell slots...

In general, though, you sort of have to be careful about this encounter. The players can get some significant boons going into the fight, but if you optimize Acererak too hard, that could end up counting for very little. I've seen people talk about alternate spell strategies for him previously that could pretty much instantly wipe a party before they could even act.

[Dungeon-noob]

Okay, so a few questions. First, why are his stats so high, compared to other Demiliches? A 27 INT, 7 above normal? A CON literally double the standard? Lower DEX and changed damage resistances for some reason? And how did a Wizard get friggin expertise? These stats feel like they were ported from 3.5 instead of made for 5e, especially the skills. The highest skill bonus i can find while tramping throught the archdevil and demon lord lists is Zariel with a +18, no expertise. Most of those CR20+ monsters don't reach +15. A +22 bonus is ludicrious, especially for something that isn't a friggin (demi)god.

Now on to strategies. I see a major weakness here that can be exploited by a 1st (!) level spell: entangle. His STR save is a grand +1, and he isn't immune to being restrained. Entangle is a STR save or be restrained, and that's just the easiest way to abuse that weakness. Given that you seem to be trying to make Archerak the 3.5 type batman/god wizard here, i find it odd that freedom of movement isn't cast before battle.

[Unoriginal]

Okay, so a few questions. First, why are his stats so high, compared to other Demiliches? A 27 INT, 7 above normal? A CON literally double the standard? Lower DEX and changed damage resistances for some reason? And how did a Wizard get friggin expertise?

He's a millenia-old, multiple-planes-and-worlds-exploring Wizard who does nothing but gather knowledge and create dungeons to kill people, and who literally beat gods. For his stats, he could just read Tomes of Stat Boosting repeatedly (as time is hardly a concern for him).

He's also a Lich, in this statblock, not a Demilich.

If you want a PC Wizard with expertise, use the Prodigy feat.

These stats feel like they were ported from 3.5 instead of made for 5e, especially the skills.

Yeah, no. There's nothing 3.5 about it.

The highest skill bonus i can find while tramping throught the archdevil and demon lord lists is Zariel with a +18, no expertise. Most of those CR20+ monsters don't reach +15. A +22 bonus is ludicrious, especially for something that isn't a friggin (demi)god.

Acererak canonically is in the demigod weight class. Could've become a god, but he has no interest in it (probably because he knows he'd be ****ed if he went through apotheosis).

Technically the highest bonus with proficiency is Tiamat's with a +26 (no expertise).

Now on to strategies. I see a major weakness here that can be exploited by a 1st (!) level spell: entangle. His STR save is a grand +1, and he isn't immune to being restrained. Entangle is a STR save or be restrained, and that's just the easiest way to abuse that weakness.

It's been noted, yes.

Given that you seem to be trying to make Archerak the 3.5 type batman/god wizard here, i find it odd that freedom of movement isn't cast before battle.

Making Acererak a "3.5 type batman/god wizard" would be a mistake, IMO. An fundamental part of his characterization is that he is unable to see the adventurers as dangerous, and he shows up unprepared because he rushes as soon as his alarm is raised.

[Asmotherion]

Even avoiding the backfiring effects, "any 8th or lower spell as a standard action" is a pretty potent thing to pass up. Especially for a ridiculous creature that has TWO ninth level spell slots...

In general, though, you sort of have to be careful about this encounter. The players can get some significant boons going into the fight, but if you optimize Acererak too hard, that could end up counting for very little. I've seen people talk about alternate spell strategies for him previously that could pretty much instantly wipe a party before they could even act.

it's too potent for there to be any chance at winning.

An example would be Replicating Druid Grove through Wish. Now the players not only have to worry about the super powerful Lich. They are unable to see (thus effectivelly target him with spells)/slowed and have to worry about extra hazards and 4 new creatures into the encounter all wile he in at his full power and retains his Legendary Actions.

Or a Mirage Arcane and the limit is pretty much the DM's creativity.

All that as a standard action.

And even a counterspell has a high chance at failing. PCs are not supposed to have access to Wish or 9th level spells when facing him (they're only level 11 after all).

Ultimatelly giving him access to Wish pretty much ensures the PCs have no way of winning through non DM interferance.

Possible, but he seems the kind to search for mighty rituals to do the job, instead. Acererak isn't afraid of waiting to accomplish his goals, and I don't see him keen to rely on something that could backfire like Wish.

From the cannon spells i can only imagine he at least used Wish and Gate for some of his accomplishments. i'm speculating possibly a ritual were several casters used Wish simultaneusly for the same goal to "overcharge" the effect.

[Unoriginal]

From the cannon spells [/FONT]i can only imagine he at least used Wish and Gate for some of his accomplishments. i'm speculating possibly a ritual were several casters used Wish simultaneusly for the same goal to "overcharge" the effect.

What makes you imagine that?

There are plenty of rituals that are at minimum as strong as Wish, and that don't require casters to cast Wish simultaneously (which would be a very impractical way of doing things).

The Volo's mentions several Yuan-ti rituals that can only be countered by Wish, for example, and many things in the Tomb of Annihilation fits that mold.

[Dungeon-noob]

He's a millenia-old, multiple-planes-and-worlds-exploring Wizard who does nothing but gather knowledge and create dungeons to kill people, and who literally beat gods. For his stats, he could just read Tomes of Stat Boosting repeatedly (as time is hardly a concern for him).

He's also a Lich, in this statblock, not a Demilich.

If you want a PC Wizard with expertise, use the Prodigy feat.

Yeah, no. There's nothing 3.5 about it.

Acererak canonically is in the demigod weight class. Could've become a god, but he has no interest in it (probably because he knows he'd be ****ed if he went through apotheosis).

Technically the highest bonus with proficiency is Tiamat's with a +26 (no expertise).

It's been noted, yes

Making Acererak a "3.5 type batman/god wizard" would be a mistake, IMO. An fundamental part of his characterization is that he is unable to see the adventurers as dangerous, and he shows up unprepared because he rushes as soon as his alarm is raised.

Okay, so we're talking about a demidiety in terms of power. Adjusting expectations accordingly.

Though he definetly feels more 3.5 to me, with those redonkilous bonuses, multiple high level buffs, tons of immunities,non-pc levels of spell slots and nasty tactics.

I'm still not quite sure about some of these stats. Natural AC 21 is the same as Zariel, CR 26 frontline powerhouse, and that feels wrong. A wizard shouldn't have the same AC as a frontline combatent, nor do i see how Arc raised his natural AC by 4. Considering he has shield at will, this makes me rather wondering how bounded accuracy is supposed to still apply here. Or aquired expertise, since NPCs don't seem to get feats by my recollection.

(And how does Tiamat get that bonus without expertise? Pretty much all NPCs i've seen in the books adhere to the same skill calculations, so either stat, stat+prof(prof consistent across statblock, often seen in the attacks), or very rarely stat+2*prof. I'm not saying you have to be wrong, just that i don't see how it'd work, and it seems counter to what i've seen from 5e so far.)

Since he's not supposed to be the batman type, i guess the other vulnerability to dex saves is also not a problem? It would leave him fairly weak against the heavier damage spells, like Fireball for lower spells, or Disintegrate or Meteor Swarm.

[bc56]

What makes you imagine that?

There are plenty of rituals that are at minimum as strong as Wish, and that don't require casters to cast Wish simultaneously (which would be a very impractical way of doing things).

The Volo's mentions several Yuan-ti rituals that can only be countered by Wish, for example, and many things in the Tomb of Annihilation fits that mold.

The adventure actually specifies that he used Wish for one of the defenses.

The beholder, Belchorzh (pronounced BEL-korj), floats at the top of the room. Acererak cast a wish spell to render Belchorzh invisible.

Emphasis theirs.

However, I would never, never give an enemy caster wish if the PCs don't have it. The ability to instantly reproduce any 8th level or lower spell is huge, since he could use whatever spell would be the deadliest at that instant.
Ones like incendiary cloud spring to mind immediately, since it would provide both cover and a lot of damage.

[Unoriginal]

The adventure actually specifies that he used Wish for one of the defenses.

Emphasis theirs.

Thank you. I had forgotten this part of the adventure.


He just doesn't have it prepared at the time of the fight, then. Which is more than reasonable.

[Asmotherion]

What makes you imagine that?

There are plenty of rituals that are at minimum as strong as Wish, and that don't require casters to cast Wish simultaneously (which would be a very impractical way of doing things).

The Volo's mentions several Yuan-ti rituals that can only be countered by Wish, for example, and many things in the Tomb of Annihilation fits that mold.

i just figured this seemed as the most staight forward solution. That plus i don't really recall anything about yuan-ti rituals. Have to check that one out.

Okay, so we're talking about a demidiety in terms of power. Adjusting expectations accordingly.

Though he definetly feels more 3.5 to me, with those redonkilous bonuses, multiple high level buffs, tons of immunities,non-pc levels of spell slots and nasty tactics.

I'm still not quite sure about some of these stats. Natural AC 21 is the same as Zariel, CR 26 frontline powerhouse, and that feels wrong. A wizard shouldn't have the same AC as a frontline combatent, nor do i see how Arc raised his natural AC by 4. Considering he has shield at will, this makes me rather wondering how bounded accuracy is supposed to still apply here. Or aquired expertise, since NPCs don't seem to get feats by my recollection.

(And how does Tiamat get that bonus without expertise? Pretty much all NPCs i've seen in the books adhere to the same skill calculations, so either stat, stat+prof(prof consistent across statblock, often seen in the attacks), or very rarely stat+2*prof. I'm not saying you have to be wrong, just that i don't see how it'd work, and it seems counter to what i've seen from 5e so far.)

Since he's not supposed to be the batman type, i guess the other vulnerability to dex saves is also not a problem? It would leave him fairly weak against the heavier damage spells, like Fireball for lower spells, or Disintegrate or Meteor Swarm.

The standard AC for an Abjuration Wizard or any Gish Caster able to use some Armor and a Shield really is around 20. Goes to 25 when calculating the Shield Spell. The fact he is animated by negative energy and his body is mostly bone gives him some natural and some supernatural armor; Since he's not going to wear any form of armor his high natural armor does not affect the game.

it's not Breaking the Game either. it's just that unlike popular belief casters are not necesserally designed to be squishy as a balancing factor.

Finally if you've been around in 3.5 you'll remember that a Lich being vulnerable to Disintegrate is more or less what the designers intended. it was after all one of the few spells that could harm a Lich. That said it's probably not the best use of the party's only 6th level spell slot.

[glasseskid93]

Okay, so a few questions. First, why are his stats so high, compared to other Demiliches? A 27 INT, 7 above normal? A CON literally double the standard? Lower DEX and changed damage resistances for some reason? And how did a Wizard get friggin expertise? These stats feel like they were ported from 3.5 instead of made for 5e, especially the skills. The highest skill bonus i can find while tramping throught the archdevil and demon lord lists is Zariel with a +18, no expertise. Most of those CR20+ monsters don't reach +15. A +22 bonus is ludicrious, especially for something that isn't a friggin (demi)god.

Now on to strategies. I see a major weakness here that can be exploited by a 1st (!) level spell: entangle. His STR save is a grand +1, and he isn't immune to being restrained. Entangle is a STR save or be restrained, and that's just the easiest way to abuse that weakness. Given that you seem to be trying to make Archerak the 3.5 type batman/god wizard here, i find it odd that freedom of movement isn't cast before battle.

That's the Acererak stat-block from the book. I didn't change anything aside from his prepped spells and giving him some winged boots. The expertise is from the Staff of the Forgotten One, and I'm not necessarily looking for a TPK, so some availability to shift the battle in their favour is beneficial. I've done some other shenanigans with his tactics (considering I hurdured and forgot greater invisibility can't be broken aside from breaking his concentration) and adjusted his prepped spells (as I hurdured again and forgot that you don't have to prep cantrips like in Pathfinder).

[bc56]

That's the Acererak stat-block from the book. I didn't change anything aside from his prepped spells and giving him some winged boots. The expertise is from the Staff of the Forgotten One, and I'm not necessarily looking for a TPK, so some availability to shift the battle in their favour is beneficial. I've done some other shenanigans with his tactics (considering I hurdured and forgot greater invisibility can't be broken aside from breaking his concentration) and adjusted his prepped spells (as I hurdured again and forgot that you don't have to prep cantrips like in Pathfinder).

One thing to note is that any possessed PCs get some pretty huge buffs when Acererak appears, and he flees when reduced to 100 hp.
The trickster spirits give the PCs 50 thp per turn and extra psychic damage on attacks. I wouldn't worry about Acererak being too powerful.

[JackPhoenix]

As I understand it, Acererak isn't loaded for a fight. He may have been chilling in whatever lair he uses at the moment, noticed someone broke his toy, so he teleported in to destroy the intruders despite not being properly prepared to battle, and gets out if he finds the PCs more trouble than he can deal with at the moment. It's not like he's got anything to lose.

He'll be better prepared for the promised second round.

[Skylivedk]

[Referring to Wish, my snip]
He just doesn't have it prepared at the time of the fight, then. Which is more than reasonable.

Nothing reasonable about not preparing the most versatile spell in existence. Especially not considering his age and intelligence.

To OP: I think you have two good approaches:
A) the sandbox: what would he have prepared on a non-combat day?
B) the spotlight: which spells make for the most fun encounter?

[dave2008]

I found Acererak's spell compliment is somewhat... off. Arcane lock and knock? Really? A multidimensional Lich capable of capturing and creating Gods has those spells prepared when he travels through the Abyss and Nine Hells to catch servants? And not wish?! I know wish can be pretty nasty, as it tanks your strength score and gives you some gnarly sicknesses, but we're talking about Acererak here. That in mind, I took some liberties with the spell prepped and his combat tactics, gave him some fancy new kicks and wanted some input on it:

Spoiler: PLAYERS BEWARE!

Show

Acererak
Medium undead, neutral evil
Armour Class 21 (natural armour)
Hit Points 285 (20d8+60)
Speed 30 ft., fly 30 ft.

Str 13 (+1) Dex 16 (+3) Con 20 (+5) Int 27 (+8) Wis 21 (+5) Cha 20 (+5)

Saving Throws Con +12, Int +15, Wis +12
Skills Arcana +22, History +22, Insight +12, Perception +12, Religion +15
Damage Resistances cold, lightning
Damage Immunities necrotic, poison, psychic (from mind blank); bludgeoning, piercing, and slashing damage from nonmagical attacks
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, paralyzed, petrified, poisoned, stunned
Other Immunities emotion and thought detection, divination spells (from mind blank)
Senses truesight 120 ft., passive Perception 22
Languages Abyssal, Common, Draconic, Dwarvish, Elvish, Giant, Infernal, Old Tongue, Primordial, Undercommon
Challenge 23 (50,000 XP)

Special Equipment. Acererak carries the Staff of the Forgotten One (with 5 charges). He wears winged boots and a talisman of the sphere with a sphere of annihilation.
Legendary Resistance (3/Day). If Acererak fails a saving throw, he can choose to succeed it instead.
Rejuvination. When Acererak is destroyed, he will gain a new body in 1d10 days, provided he has a phylactery, regaining all his hit points and becoming active again. The new body appears within 5 feet of the phylactery, the location of which is hidden.
Spellcasting. Acererak is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 23, +15 to hit with spell attacks). Acererak has the following wizard spells prepared:
Cantrips (at-will): chill touch, mage hand, toll the dead
1st-level (at-will): comprehend languages, identify, magic missile, shield
2nd-level (at-will): blindness/deafness, detect thoughts (c)
3rd-level (at-will): counterspell, dispel magic, lightning bolt, speak with dead
4th-level (3 slots): blight, greater invisibility (c)
5th-level (3 slots): legend lore, synaptic static
6th-level (3 slots): disintegrate, soul cage
7th-level (3 slots): finger of death, force cage, teleport, plane shift, power word pain
8th-level (2 slot): feeblemind, mind shield*
9th-level (2 slot): foresight*, wish
* Cast before combat
Turn Resistance. Acererak has advantage on saving throws against any effects that turns undead.

Actions
Paralyzing Touch. Melee Spell Attack: +12 to hit, reach 5 ft., one creature. Hit: 10 (3d6) cold damage, and the target must succeed a DC 20 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on a success. This attack’s spellcasting ability is Charisma. (I saw that it was a spell attack that used strength to hit, so after taking a look at his stats I decided to use charisma as the "spellcasting ability". It was between that and constitution, so I'm open to thoughts.)
Staff (+3 Quarterstaff). Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 7 (1d6+4) bludgeoning damage plus 10 (3d6) necrotic damage, or 8 (1d8+4) bludgeoning damage plus 10 (3d6) necrotic damage when used in two hands.
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 a DC 23 saving throw or be cursed. Until the curse is removed. The target can’t regain hit points and has vulnerability to necrotic damage. Greater restoration, remove curse, or similar spell ends the curse on the target.

Legendary Actions
Acererak can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. Acererak regains spent legendary actions at the start of his turn.
At-Will Spell. Acererak casts one of his at-will spells.
Melee Attack. Acererak uses Paralyzing Touch or makes one melee attack with his staff.
Frightening Gaze (Costs 2 Actions). Acererak fixes his gaze on one creature he can see within 10 feet of him. The target must succeed a DC 20 Wisdom saving throw or become frightened for 1 minute. The target can repeat this saving throw at the end of each of its turns, ending the effect on itself on a success. If the target’s saving throw is successful or the effect ends for it, the target is immune to Acererak’s gaze for 24 hours.
Talisman of the Sphere (Costs 2 Actions). Acererak uses his talisman of the sphere to move the sphere of annihilation under his control up to 90 feet.
Disrupt Life (Costs 3 Actions). Each creature within 20 feet of Acererak must make a DC 20 Constitution saving throw, taking 42 (12d6) necrotic damage on a failed save, or half as much on a successful one.

Tactics
Before Combat. Acererak casts foresight and mind blank at the beginning of each day to ensure he is prepared for all threats before him.
During Combat. Acererak opens by activating his winged boots and casting greater invisibility to analyze the enemy force. On subsequent turns, he moves randomly through the battlefield to maintain confusion while using his talisman of the sphere and sphere of annihilation to harass the enemies. After identifying the arcane caster, he moves to an advantageous position and casts feeblemind on the caster. Should the caster save, he casts power word pain on his next turn, attempting to incapacitate the arcane caster first.
Now visible, he maintains an advantageous position as best he can and casts forcecage in the box format, attempting to capture any further casters in the party. He shifts to debilitating further party members using the curse effect from his Staff of the Forgotten One. He then begins harassing the group further, using spells as necessary to eliminate as many threats as possible, such as targeting fighters with lightning bolt and rogues with blindness/deafness.
Should an enemy die and his reaction be available, Acererak will cast soul cage to maintain the advantage over the party, generally using it to keep his hit points as high as possible. Otherwise, he will use his reaction to cast counterspell, but never above 3rd-level, as he is confident that he will be powerful enough to dispel any magic the mortals could cast.

I rolled for the current charges in the Staff. My party's heading into the final room on Tuesday, and the current setup is a shadow monk/champion fighter, death domain cleric, war wizard, storm domain cleric, and path of ancients paladin.

Yes, to me they gave him a general spell list for any given day. However, I feel he has to know the adventurer's are coming and he is preparing to wipe them out. I approve of the buffed up spell list.

[Unoriginal]

However, I feel he has to know the adventurer's are coming and he is preparing to wipe them out.

In ToA, he specifically DOESN'T know that.

[bc56]

In ToA, he specifically DOESN'T know that.

Even if he does, his flaw is that he underestimates his opponents. He would expect the PCs to be killed by the tomb, or the Sewn Sisters, or the Atropal.

[Malifice]

I found Acererak's spell compliment is somewhat... off. Arcane lock and knock? Really? A multidimensional Lich capable of capturing and creating Gods has those spells prepared when he travels through the Abyss and Nine Hells to catch servants? And not wish?! I know wish can be pretty nasty, as it tanks your strength score and gives you some gnarly sicknesses, but we're talking about Acererak here. That in mind, I took some liberties with the spell prepped and his combat tactics, gave him some fancy new kicks and wanted some input on it:

Spoiler: PLAYERS BEWARE!

Show

Acererak
Medium undead, neutral evil
Armour Class 21 (natural armour)
Hit Points 285 (20d8+60)
Speed 30 ft., fly 30 ft.

Str 13 (+1) Dex 16 (+3) Con 20 (+5) Int 27 (+8) Wis 21 (+5) Cha 20 (+5)

Saving Throws Con +12, Int +15, Wis +12
Skills Arcana +22, History +22, Insight +12, Perception +12, Religion +15
Damage Resistances cold, lightning
Damage Immunities necrotic, poison, psychic (from mind blank); bludgeoning, piercing, and slashing damage from nonmagical attacks
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, paralyzed, petrified, poisoned, stunned
Other Immunities emotion and thought detection, divination spells (from mind blank)
Senses truesight 120 ft., passive Perception 22
Languages Abyssal, Common, Draconic, Dwarvish, Elvish, Giant, Infernal, Old Tongue, Primordial, Undercommon
Challenge 23 (50,000 XP)

Special Equipment. Acererak carries the Staff of the Forgotten One (with 5 charges). He wears winged boots and a talisman of the sphere with a sphere of annihilation.
Legendary Resistance (3/Day). If Acererak fails a saving throw, he can choose to succeed it instead.
Rejuvination. When Acererak is destroyed, he will gain a new body in 1d10 days, provided he has a phylactery, regaining all his hit points and becoming active again. The new body appears within 5 feet of the phylactery, the location of which is hidden.
Spellcasting. Acererak is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 23, +15 to hit with spell attacks). Acererak has the following wizard spells prepared:
Cantrips (at-will): chill touch, mage hand, toll the dead
1st-level (at-will): comprehend languages, identify, magic missile, shield
2nd-level (at-will): blindness/deafness, detect thoughts (c)
3rd-level (at-will): counterspell, dispel magic, lightning bolt, speak with dead
4th-level (3 slots): blight, greater invisibility (c)
5th-level (3 slots): legend lore, synaptic static
6th-level (3 slots): disintegrate, soul cage
7th-level (3 slots): finger of death, force cage, teleport, plane shift, power word pain
8th-level (2 slot): feeblemind, mind shield*
9th-level (2 slot): foresight*, wish
* Cast before combat
Turn Resistance. Acererak has advantage on saving throws against any effects that turns undead.

Actions
Paralyzing Touch. Melee Spell Attack: +12 to hit, reach 5 ft., one creature. Hit: 10 (3d6) cold damage, and the target must succeed a DC 20 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on a success. This attack’s spellcasting ability is Charisma. (I saw that it was a spell attack that used strength to hit, so after taking a look at his stats I decided to use charisma as the "spellcasting ability". It was between that and constitution, so I'm open to thoughts.)
Staff (+3 Quarterstaff). Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 7 (1d6+4) bludgeoning damage plus 10 (3d6) necrotic damage, or 8 (1d8+4) bludgeoning damage plus 10 (3d6) necrotic damage when used in two hands.
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 a DC 23 saving throw or be cursed. Until the curse is removed. The target can’t regain hit points and has vulnerability to necrotic damage. Greater restoration, remove curse, or similar spell ends the curse on the target.

Legendary Actions
Acererak can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. Acererak regains spent legendary actions at the start of his turn.
At-Will Spell. Acererak casts one of his at-will spells.
Melee Attack. Acererak uses Paralyzing Touch or makes one melee attack with his staff.
Frightening Gaze (Costs 2 Actions). Acererak fixes his gaze on one creature he can see within 10 feet of him. The target must succeed a DC 20 Wisdom saving throw or become frightened for 1 minute. The target can repeat this saving throw at the end of each of its turns, ending the effect on itself on a success. If the target’s saving throw is successful or the effect ends for it, the target is immune to Acererak’s gaze for 24 hours.
Talisman of the Sphere (Costs 2 Actions). Acererak uses his talisman of the sphere to move the sphere of annihilation under his control up to 90 feet.
Disrupt Life (Costs 3 Actions). Each creature within 20 feet of Acererak must make a DC 20 Constitution saving throw, taking 42 (12d6) necrotic damage on a failed save, or half as much on a successful one.

Tactics
Before Combat. Acererak casts foresight and mind blank at the beginning of each day to ensure he is prepared for all threats before him.
During Combat. Acererak opens by activating his winged boots and casting greater invisibility to analyze the enemy force. On subsequent turns, he moves randomly through the battlefield to maintain confusion while using his talisman of the sphere and sphere of annihilation to harass the enemies. After identifying the arcane caster, he moves to an advantageous position and casts feeblemind on the caster. Should the caster save, he casts power word pain on his next turn, attempting to incapacitate the arcane caster first.
Now visible, he maintains an advantageous position as best he can and casts forcecage in the box format, attempting to capture any further casters in the party. He shifts to debilitating further party members using the curse effect from his Staff of the Forgotten One. He then begins harassing the group further, using spells as necessary to eliminate as many threats as possible, such as targeting fighters with lightning bolt and rogues with blindness/deafness.
Should an enemy die and his reaction be available, Acererak will cast soul cage to maintain the advantage over the party, generally using it to keep his hit points as high as possible. Otherwise, he will use his reaction to cast counterspell, but never above 3rd-level, as he is confident that he will be powerful enough to dispel any magic the mortals could cast.

I rolled for the current charges in the Staff. My party's heading into the final room on Tuesday, and the current setup is a shadow monk/champion fighter, death domain cleric, war wizard, storm domain cleric, and path of ancients paladin.

Seeing as he can cast it at will as a legendary action, you might want to give him the Blade ward cantrip.

For the price of a single legendary action each round (of which he has 3) he gains resistance to B, S and P damage from weapons, without affecting his concentration.

Even magical ones.

He really needs wall of force, mirror image and globe of invulnerability. They're literally three of the best spells in the game.

Id also strip Wish off him (it's not needed for a BBEG) and would replace it with something else. Time Stop; or if you want to get really nasty, Psychic scream (DC 23 Int save or be stunned anyone?).