How to prepare my party to reasonable be able to bring down a prismatic wall?


Background

In my campaign I have a villain who uses misdirection and avoidance as their main combat methods. As 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 7 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 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 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 0. 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 5 out of the 7 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.