Since it's tangentially related, here's my current draft for Sunday's game, where the team of six level 14 heroes will face Acecerak.
Unlike most other monsters of the module, I didn't need to beef him up
Of course, his listed spell load out is basically drained down the toilet, and replaced with a more flashy and impressive one. His biggest change is that unless the heroes are particularly unlucky, I plan to give him one legendary action per hero (=6), just as I have done in general for legendary creatures.
As discussed, the trickster god bonus has been supplemented with one +12 save each round. (The specific reason to add it was the Psychic Scream spell suggestion, which I ended up not using).
Acecerak's Tactics
At the end of the round where the heroes injure either the Atropal or the Soulmonger (“round zero”), Acecerak shifts in - and the trickster gods immediately start shrieking. He arrives invisible*, and with Sadamor's Sphere of Annihilation (medium-sized, so to avoid the save) in tow. This in turn triggers the trickster god abilities: 50 temporary hit points at the start of each round plus the ability to let the trickster god handle one saving throw each round (at +12).
His actual location is the southern-most balcony, but unless he rolls a 1 on his Time Stop die, he attempts to fool the party into believing he appears on the strut of the Soulmonger (like in the illo).
At the start of round 1, roll initiative for Acecerak. He has advantage* on the roll.
*) item if you want to explain these abilities: Give Acecerak a "Ring of Accelerated Invisibility" (legendary, requires attunement). As per ring of invisibility, plus you gain advantage on initiative rolls. (Acecerak had one attunement slot free.)
Round #1: Cast time stop (remember, you are hopefully invisible and can't be counterspelled). Then cast 2-5 spells:
First: prismatic wall (sphere, 30 ft diameter) above the heads of the heroes
(Second): mislead* (to appear as if on an adamantine strut per the illustration while in reality not doing anything as foolish; plus go invisible again to prevent getting counterspelled)
The intended result here is for Acecerak to appear on the strut as if he has always been there, and that he just became visible for casting spells. Even if the illusion only soaks a single character's attacks, that counts as a success in a murderuously intense fight like a lich fight
(Third): forcecage (catch one or two heroes: preferably ones not under prismatic sphere)
(Fourth): mirror image
Last: reverse gravity (ending the time stop).
Damage: 55 (10d10) fire damage (no save) in the reverse gravity area. Creatures below the prismatic sphere:
- Con save or be blinded
- dex save for 35 (10d6) fire damage or half
- dex save for 35 (10d6) acid damage or half
- dex save for 35 (10d6) lightning damage or half
- dex save for 35 (10d6) poison damage or half
- dex save for 35 (10d6) cold damage or half
- dex save or be restrained (three con saves to be free or petrified)
- dex save or be blinded, and wis save or be cast into the ethereal plane*
Total possible average damage 55 + 175 damage (better make some of those saves!)
*) the spell offers Astral as an alternative, but given Acecerak's protections on the Tomb, I think ethereal is actually the logical choice
At-will 1st through 3rd level spells:
Dispel Magic (if bothered by a particular effect)
Invisibility (cast it after a PC's turn before a spellcaster's turn)
Mirror Image (cast it after a PC's turn before a melee bruiser's turn)
Misty Step (cast it to escape grappled)
...as decidedly secondary choices
Lightning Bolt (cast to harass PCs)
Legendary actions analysis (with six actions against six heroes, the 2 or 3 cost actions aren't actually as bad):
At-Will Spells: great, see above
Melee Attack (option Paralyzing touch): not so great, unless both Druid and Paladin is taken out of the picture (and thus can't trivially cure the paralyzed condition). Paralyzing touch has a low to-hit bonus. It must be targeted at a low-AC creature that still wants to come close, and must be followed-up with something targeting a Strength or Dexterity save to be
really effective. I suggest Chain Lightning or Disintegrate.
Melee Attack (option staff bash): Invoke Curse and attacking with the staff is way too slow in this encounter. In a completely different kind of fight (a much larger and therefore longer one), I can see this as a fall-back option against magic-immune foes.
Frightening Gaze (2): possibly, if a melee bruiser is inching closer.
Talisman of the Sphere (2): only to annihilate those stupid enough to not only attack him in melee
but stay around afterwards (I will make the danger clear). Make an Int (Arcana) DC 25 check with a bonus of +22. I will use a reduced range, however - the point isn't to give Acecerak a 90 ft range instadeath button!* I'm thinking 20-30 feet, tops.
*) Could it be that the ToA writers have misinterpreted the Talisman of the Sphere? It does allow an effect that with Ace's stats becomes 90 ft but that effect is levitate, which is vertical, not horizontal, movement.
Anyhoo - since this particular Sphere is larger, nothing says it can't be slower too.
Disrupt Life (3): generally not worth it because its up the flexibility of having an action behind every hero; maybe when 3+ heroes can be caught in the effect - if and only if that ever happens. 42 (12d6) necrotic damage; DC 20 Con save for half.
Reaction: counterspell, unless only warriors left, then shield. In other words, Acecerak won't spend his only reaction on Shield unless he's reasonably sure it will be his turn before any spellcasters. (Remember that he's old school - respecting and fearing magic MUCH more than martial opponents
as if he still played 3E )
Subsequent rounds:
He won't waste his main action on anything he can do through Legendary Actions. Translation:
cast a spell of higher level than three every round!
I suggest Power Word Stun (ideally at a spellcaster; remember temporary hp doesn't save you)
Try to avoid Concentration spells, since even with a +12 Con save, he will lose Concentration sooner or later. Dominate Monster* and Banishment* are among the more effective ones.
Unlike the book Acecerak my lich won't flee. If it's his turn and death is imminent, he won't teleport away. Instead he will move towards as many characters as possible and then break his staff (=132 (24d10) force damage, DC 18 Dex save for half) to spite the players (who will never know the staff is basically useless to them*).
*) I did read over at rpg stack exchange that protection from good and evil presents a good case for shielding yourself from the staff's possession. If they unlikely happens they manage to snatch it from him.
