A shimmering, multicolored plane of light forms a vertical opaque wall--up to 90 feet long, 30 feet high, and 1 inch thick--centered on a point you can see within range. Alternatively, you can shape the wall into a sphere up to 30 feet in diameter centered on a point you choose within range. The wall remains in place for the duration. If you position the wall so that it passes through a space occupied by a creature, the spell fails, and your action and the spell slot are wasted.
The wall sheds bright light out to a range of 100 feet and dim light for an additional 100 feet. You and creatures you designate at the time you cast the spell can pass through and remain near the wall without harm. If another creature that can see the wall moves to within 20 feet of it or starts its turn there, the creature must succeed on a Constitution saving throw or become blinded for 1 minute.
The wall consists of seven layers, each with a different color. When a creature attempts to reach into or pass through the wall, it does so one layer at a time through all the wall's layers. As it passes or reaches through each layer, the creature must make a Dexterity saving throw or be affected by that layer's properties as described below.
The wall can be destroyed, also one layer at a time, in order from red to violet, by means specific to each layer. Once a layer is destroyed, it remains so for the duration of the spell. Antimagic field has no effect on the wall, and dispel magic can affect only the violet layer.
1. Red. The creature takes 10d6 fire damage on a failed save, or half as much damage on a successful one. While this layer is in place, nonmagical ranged attacks can't pass through the wall. The layer can be destroyed by dealing at least 25 cold damage to it.
2. Orange. The creature takes 10d6 acid damage on a failed save, or half as much damage on a successful one. While this layer is in place, magical ranged attacks can't pass through the wall. The layer is destroyed by a strong wind.
3. Yellow. The creature takes 10d6 lightning damage on a failed save, or half as much damage on a successful one. This layer can be destroyed by dealing at least 60 force damage to it.
4. Green. The creature takes 10d6 poison damage on a failed save, or half as much damage on a successful one. A passwall spell, or another spell of equal or greater level that can open a portal on a solid surface, destroys this layer.
5. Blue. The creature takes 10d6 cold damage on a failed save, or half as much damage on a successful one. This layer can be destroyed by dealing at least 25 fire damage to it.
6. Indigo. On a failed save, the creature is restrained. It must then make a Constitution saving throw at the end of each of its turns. If it successfully saves three times, the spell ends. If it fails its save three times, it permanently turns to stone and is subjected to the petrified condition. The successes and failures don't need to be consecutive; keep track of both until the creature collects three of a kind. While this layer is in place, spells can't be cast through the wall. The layer is destroyed by bright light shed by a daylight spell or a similar spell of equal or higher level.
7. Violet. On a failed save, the creature is blinded. It must then make a Wisdom saving throw at the start of your next turn. A successful save ends the blindness. If it fails that save, the creature is transported to another plane of the GM's choosing and is no longer blinded. (Typically, a creature that is on a plane that isn't its home plane is banished home, while other creatures are usually cast into the Astral or Ethereal planes.) This layer is destroyed by a dispel magic spell or a similar spell of equal or higher level that can end spells and magical effects.
I love that the wall, for all of its effects and failsafes, is completely vulnerable to blind teleportation (i. e. Dimension Door) or interplanar travel (i. e. Etherealness) in a way that Forcecage, a 7th level spell, just isn't.
I'm a 2nd Edition player, and am learning the 5th Edition rules. The "Illusionist" PC was always my favorite because most folks didn't know how to play said PC, but if you learn how it's as effective and perhaps mores than any of the PCs.
Taste the Rainbow
Only works if there is nothing on the ground that the BBEG could hold on to. Otherwise, he will just use his legendary resistance to save against reverse gravity and then you just wasted your 9th level spell for a fancy floating disco orb. ;)
The indigo layer stops dimension door from being cast through the wall. Etherealness does work, but only for one pass, and not a lot of enemies have that spell.
In any case, this is mostly a defensive spell. Set up a perimetre, cover yourself with the wall, then pop out to attack enemies before popping back in. You can even leave yourselves a recess outside the wall to retreat to should an enemy breach the wall, effectively trapping the enemy inside.
Seems to me that the Reverse Gravity combination that's been mentioned here in the comments wouldn't work because the first sentence specifies the wall is vertical. You could I suppose try to favorably interpret what is meant when the spell describes a 90 foot long and 30 foot high vertical wall, but seems pretty clear to me that it means at a 90 degree angle relative to the horizontal plane of, well, the ground. As a DM, I would need to at least see a Spider Climb spell get involved before I would allow such a wombo-combo. ;)
the next line. "Alternatively, you can shape the wall into a sphere up to 30 feet in diameter centered on a point you choose within range."
On the indigo layer, "If [the creature] successfully saves three times, the spell ends."
This is a copy-paste error, right? Otherwise the Violet layer would never be triggered by creatures entering from the outside.
Prismatic Wall doesn’t require concentration. The rule you linked specifically references trying to cast two concentration spells.
There are a number of other issues with the combo, but concentration rules isn’t one.