I'd been running the Adventurers League adventures for Tomb of Annihilation, but when I got to the point where the death curse was over, I realized that the players would feel cheated if they weren't the ones to stop it. As such, I had them go to the Tomb of the Nine Gods, and since it's mainly traps and puzzles, it's been a pretty good challenge for them.
What I'm worried about is whether or not the final encounter with Acererak and the atropal will be a cakewalk for them, so I figured I should increase the challenge. I've noticed that they tend to tear through encounters that consist of only a couple enemies, so I'm wondering if increasing the number of NPCs is the best way to go. Perhaps I could increase the number of wraiths created by the atropal during a round, and have them absorb any damage to the atropal? What are some other ideas?
The biggest problem you face as I see it as a level 16 party might trivialise the Atropal. So where the party is meant to be on the ropes, they'll be not only fresh but also potentially super-buffed by the trickster gods. One option would be to have him present with
the Atropal. Who knows what kinds of divination magic he can access: maybe he knows what's coming! I suspect the two together might be quite a hard fight.
I have a party exploring the Tomb at present, and have given some thought to Acererak. Seing as I use Fantasy Grounds VTT, it's easy for me to clone the campaign and test my ideas. Some notes for you
- I found that the Atropal should just spam its exhaustion effect. Exhausted characters don't have nearly as good a time with Acererak and they (almost certainly) lack time to recover from exhaustion before the fight. Remember it can legendary action this, so it goes right after the first PC meaning it should get at least one cast off.
- Acererak arrives standing in front of a portal. If he needs to, he should back out through it and rethink his approach... and then return!
- I gave Acererak a contingency of a banishment spell (target self), so that worst case he can bug out and rethink as above.
- I tried having Acererak's first cast be psychic scream (XGE), but found that too powerful. The problem is that if PCs fail, they may not have good enough Int saves to ever succeed and then are just stun-locked forever. Still, it's worth considering...
I revised his spell list completely; gods know what the designers were thinking!? He can at-will fireball or hold person, why on Earth would a being as ancient and cunning as Acererak not have that sort of thing?
I decided that Acererak has a pretty good idea that he will be running into a bunch of so-called heroes, who were obviously powerful enough to murder his baby, so he arrives with a plan
Revised spell list
Cantrips (at will): frostbite, mage hand, prestidigitation
1st level (at will): absorb elements, shield
2nd level (at will): mind spike, misty step
3rd level (at will): counterspell, fireball
4th level (3 slots): banishment, greater invisibility, mordenkainen's private sanctum
5th level (3 slots): bigby's hand, scrying, seeming
6th level (3 slots): disintegrate, mass suggestion, scatter
7th level (3 slots): etherealness, forcecage, plane shift*
8th level (2 slots): abi-dalzim's horrid wilting, dominate monster, mind blank*
9th level (2 slots): time stop, wish
The plan is to time stop, greater invis himself if that seems like a good idea, and forcecage whoever he thinks is strong and likely to stay imprisoned by it. I like @dave2008
's version of Acererak, but do believe wish and forcecage are better picks. Note that I kept the same number of spells at each level as he has in the book, but obviously there isn't really a strong reason to do that. I also tried to think about what spells might make sense for him to have in mind most plane-hopping days (with a background idea that somewhere out there he has a simulacrum with all the tedious but useful spells that you really want to cast while staying at home).