Background
In my campaign I have a villain who uses misdirection and avoidance as their main combat methods. They won't fight directly, but they use summoned creatures, minion allies and illusions to avoid the party's attacks. As a last resort, when the party confronts them in their lair, it would be appropriate for them to use Prismatic Wall to prevent the party from killing or capturing them.
Prismatic Wall requires seven different, very specific, spells in a specific order to remove. Namely; Cone of Cold, Gust of Wind, Disintegrate, Passwall, Magic Missile, Daylight, and Dispel Magic.
This enemy is clever, but arrogant. They will likely cast this spell toward the end of a drawn out battle, meaning the party may already be down on resources. Without warning, they might need to defeat a Prismatic Wall, and the party may expend the required resources before it appears.
Party Details
In my party I have:
- A Half-Elf Wizard
- A Human Druid
- A Gnome Oracle
- A Halfling Bard
- A Half-Orc Paladin.
The party is currently 9th level, and they will likely confront this enemy some time between 12th and 14th level depending on how direct their approach is.
The party is equipped slightly below normal for their level due to some decisions made to this point in the campaign. None of their current items will be a particular benefit in this task.
The Wizard and Bard both have high knowledge skills that could be used for research, they have most of the knowledge skills covered between them. The Oracle and Druid have access to some divination magic which could also be used to provide information, if they know to use it.
The Problem
I would like my party to have a reasonable chance of actually being able to bring down this wall. If I just throw it at them the chance of this is basically zero. This is the first campaign for all of my players and they have never encounter anything like this before.
Between the various spellcasters in the party they already have access to five out of the seven required spells, Disintegrate and Passwall being the exceptions. I can easily provide them access to the others between now and the confrontation. However, the party does not always prepare these specific spells and may not have them available when required.
How can I, as DM, prepare my players to defeat a Prismatic Wall spell, without explicitly telling them it is coming?
I will likely need to provide them both with information on how to defeat it and provide some resources to help them do so. I am willing to provide help in the form of items, lore dumps from NPCs and potentially NPC allies, though I prefer not to have NPC perform critical actions in place of the players.
Best Answer
Give them chances to do research
As the group tracks down the villain, they might find traces of their spell research, or NPCs they have persuaded to help them create this fearsome spell. They might find their notes or even an old spellbook. Investigating these objects might reveal that the villain has this spell, and the proper way to counter it.
But honestly they can just bypass it
A dimension door spell will get the group past the wall without the need to slowly disassemble it. Depending on the group, they might also be able to collapse the ceiling and go over it, dig a hole under it, et cetera.
Think about broader tactical implications
You've said that the villain wants to use this spell toward the end of a battle. Usually when the villain is losing a battle they tend to be surrounded on all sides by melee fighters who can attack-of-opportunity them. Is the villain really going to be able to get to a clear corner to cast this wall spell?
This spell only lasts ten minutes per caster level (so less than three hours). Can the party just wait it out?
Is the villain planning to cast this spell and then run away, leaving the wall to block their retreat? If so, how does the villain flee, and how will the group track him down? And wouldn't it be simpler for the villain to use dimension door or teleport as their retreat spell?
If the party does use dimension door to get past the wall, can the villain just run through the wall (taking some attacks of opportunity, possibly) and now the party is walled off again?
If the party spends all seven of the spells to disassemble this wall, can the villain just cast another one, perhaps from a scroll?