If a creature is moved through a prismatic wall multiple times is it affected multiple times?

Question

Most similar spells like wall of fire have descriptions that specifically prevent a creature from being dealt the spell's damage multiple times per turn, but prismatic wall is worded differently.

As written, it seems like a creature could be affected by the prismatic wall multiple times during a turn. However, it's trivial for a grappler to drag an enemy through the prismatic wall, like, three times then finally shove the enemy through the wall, dealing the enemy about 700 points of damage and probably rendering the enemy petrified. This is well beyond even other 9th-level spells.

Can a creature be affected by the prismatic wall more than once per turn?

Answer 1

It's debatable whether they would be affected at all

There are numerous spells that do damage or otherwise inconvenience a creature when that creature moves, or is moved, into their area of effect. Since you used Wall of Fire as an example, let's examine the text that spell uses:

Wall of Fire

A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. (PHB, p. 285)

This movement does not need to be voluntary: if you are shoved into a Wall of Fire, or walk into it yourself, you still "enter" the wall. However, note the similar (but not identical) text of Prismatic Wall (PHB, p. 269, bold added):

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.

This "attempts" is crucial. If a creature is grappled and moved against its will, it did not "attempt" to move in the direction it is moving: it had no choice in the matter. For a creature to "attempt" to pass through the wall, it must be moving through it (or reaching into it) voluntarily.

This is also complicated by the fact that the second sentence in the quote above doesn't require intent, but simply that a creature "passes through" or "reaches through" a layer of the wall. It is a DM's prerogative to decide which of these sentences takes precedence in this situation.

What happens if you're pushed/grappled into the wall?

It's very hard to say. Strangely, none of the layers of the wall prevents a creature from physically passing through it while they are active (layers prevent things like magical and nonmagical ranged attacks from penetrating the wall). Nor is there any text that directly states that the wall is solid. It is described as "opaque", but that simply means you cannot see through it.

It would be a DM's call what would happen if you shoved a creature towards the wall, or attempted to run through the wall with a creature grappled. A case could be made for the idea that the wall is solid when you are thrown into it, because of the "attempts" mentioned mentioned earlier: this time, "attempts" is significant not because it indicates willing movement, but because it suggests a possibility of failure. If you "attempt" to move through something, it does somewhat imply that moving through it is not guaranteed, which might imply some level of solidity. Again though, that's very much a DM's call.

One thing seems clear to me: it does not seem likely that the wall is meant to be both harmless and intangible to creatures who are pushed through it involuntarily. If that were the case, a group of enemies could simply shove each other through it and avoid its effects altogether (except the unlucky one who is last).

What about the Blindness Condition?

(Credit to HellSaint for mentioning this in a comment). Passing into or through the wall is not the only way the wall could affect a creature (PHB, p. 267-269 [sic]).

...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.

This effect is one place where the rules seem somewhat clearer. The text says "moves" rather than "is moved", but forced movement is still movement. Likewise, the text of Wall of Fire requiring a character "enter" the area is similar grammatically to the text here requiring the creature to "move." And crucially, there is no text in this section restricting this particular affect to happening only the first time that a creature moves into its area on a particular turn.

Although there is no designer answer to this question as yet, the Rules As Written (RAW) seem to indicate that you could drag a creature close to the wall (within 20 feet) and subject them to the saving throw to avoid blindness. And conceivably, if the creature succeeds, you could then drag them away from the wall, and towards it again all on the same turn, subjecting them to the same saving throw once again.

Of course, you'd need to spend a 9th level spell slot to do so.

Answer 2

The Answer

First, I agree with Gandalfmeansme's answer, the debatable thing here is whether being moved through the wall counts as attempting to reach/pass through the wall or not. There is no indication that it should only happen once, and if the creature is willingly moving in and out, they should be affected by it everytime. This means either being moved through counts as a trigger everytime or never.

Restating his answer, the interpretation that being dragged does not count is based on the wording "attempts" to do something, and someone being dragged is not "attempting" to do anything, he is being forced to.

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.

And my answer for that is No, being forcibly moved through the wall does not trigger the harmful effects ¹. Besides the semantic argument that being forced to do something is not attempting to do something, which is ultimately a DM call, there are other reasons for that reading.

• Wall spells are usually intended to be battlefield-controlling spells, not burst-damaging spells. As you mentioned, allowing "being moved through" count as a trigger would lead it to be the most damaging spell in the game.
• Prismatic Wall is a huge wall (haha.) of text, and certainly some details were skipped. This answer covers well one example of very likely (imo) error on this spell.

Final Word

Obviously, the decision is up to the DM. By RAW, I would say it's unclear if being moved through the wall counts as harming the creature, and my reading on the overall archetype of the spell tells me it shouldn't be used that way. Thus, I, personally, would not allow such an "exploit".

The bonus: How much of it is simply a thought experiment?

Usually, when thinking about these exploits, it's nice to think about how likely and useful they actually are. By 17th level (which is where the spellcaster is getting Prismatic Wall if he did not multiclass) you are fighting Adult Dragons, Celestials and Balors, or at least these are the "minimum" targets for a 9th level spell. Even a Grappling build will have problems actually grappling these guys. Being able to deal 700 average damage against a goblin is no better than being able to deal 20 - the goblin dies anyway.

Other 9th level spells

I would also note that, although these are subject to DM fiat, there are other spells that certainly are more world-changing than 700 average damage.

True Polymorph allows you to create an unlimited army of Young Silver Dragons, given enough time for that (do it during your downtime) and money to feed them (you are a 17th level wizard with a Staff of Magi - you are rich). Treat them nicely while they are under your control and they should be friendly to you afterwards. Profit.

Wish is Wish. Gate is Wish - or just bringing a freaking Demigod to our plane.

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¹ This answer is simply telling you what's written and how I read it, followed by the reasons I read it this way. While this might not be the best way to rule it, for whatever reason, it is the one that has text supporting it. Repeating my point about the thought experiment: balancing is relevant for situations that will actually happen in a real table and I'm not providing an answer about something I have no experience with and with no text support.

Exploits are ultimately DM's job to solve by adjucating rules in a way that makes the game fun - if everyone wants to find exploits and explore them, go for it. If one player wants to be the smart guy exploiting the game and making everyone else unhappy, the DM will simply rule him out and tell him that's not how it works.