On the other hand, Acererak is a multi-dimension lich of impossible age who is siphoning souls in order to create a new divine being. If anyone is going to have a new spell the party hasn't heard of, it's him.
Absolutely true.
I still don't think that from the players' POV the satisfaction of witnessing a truly clever NPC will take away the sting of a single spell TPK:ing the entire party.
That's not Acecerak's concern. That's my concern. I can always kill off my party, regardless of how many boons and gadgets I give them.
But it's a matter of wobbly game design in my opinion. The actual suggestion to use the spell is great.
The way the game allows you to create a set of heroes that are completely defenseless to this new spell is not. My party does not feature a Wizard. It is possible to gain Paladin's aura, and several characters have save-boosting items, but I would still be surprised if anyone other than the rogue sports much more than a +3.
And it's not that the adventure has provided any clues that they need to boost their Int saves. And it's not that the rules allow it either: how do you actually increase your Int saves (as opposed to merely getting advantage)? How do you cure someone from the Stunned condition?
Without having done the numbers I would guess one character (the rogue, standing next to the MC pala/warlock) might reach close to an even shot at making that save, another perhaps 10%, and at least two characters will never make it even if they never roll anything but 20's.
The chance/risk of the encounter ending before it has even begun is overwhelming. The even worse risk - that it becomes a drawn-out game of cat and mouse between the lich and a skulking Rogue (also called "the game of nothing happens") while everybody else sits on their hands until either have won.
That is not a fun encounter. In fact, that is a
decidedly unfun encounter. Especially if I'm pulling a rabbit out of my hat (as it were), brining out a spell they might not have heard of before. (Some of them have purchased XGE. But we started this campaign without it, so I doubt any one of them have read through it thoroughly).
See my point? Which, BTW, is related to the poor way 5th edition handles high-level saving throw DCs, i.e. there really isn't any way to prop up your weaknesses (without unreasonably abstaining from the minmaxing players love to do; being asked to take a feat to raise your shot at making a save from 0% to 10% when those saves happen one or three times in the whole campaign is pretty frakking unreasonable). The game desperately needs a non-Concentration buff spell that allows each party member to say "know what? I think I need a higher Wisdom save for this encounter, so let's choose that". They might guess wrong, but at least there was a path you could have chosen.
And so I feel I can't use Psychic Scream in my campaign, unless it's cast by a monster whose DC falls within "bounded accuracy" (that is 10 to 20). If a Sewn Sister had had this spell, it could be fun (their DC were 16 in my version). Even if your save bonus is -1, DC 16 is still "fair game". Once the DCs go above 20, the game's disinterest in making sure play remains fair becomes a very awkward design failure.
So thanks for the suggestion, but I'll save it for another day. I hope you now see why.
