We were fighting Vecna himself, and at one point had a *[prismatic wall](https://www.dndbeyond.com/spells/prismatic-wall)* up between us and Vecna. The *prismatic wall* says it creates "a vertical, opaque wall."

Vecna's powers include truesight, and presumably x-ray vision as well (since the artifact *Eye of Vecna* allows its bearer to use x-ray vision), and the DM thought Vecna would be able to see through the prismatic wall and target us. A *[ring of x-ray vision](https://www.dndbeyond.com/magic-items/4738-ring-of-x-ray-vision)* states:

> 
> While wearing this ring, you can use an action to speak its command word. When you do so, you can see into and through solid matter for 1 minute. This vision has a radius of 30 feet. To you, solid objects within that radius appear transparent and don't prevent light from passing through them. The vision can penetrate 1 foot of stone, 1 inch of common metal, or up to 3 feet of wood or dirt. Thicker substances block the vision, as does a thin sheet of lead.
> 
> 
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So can someone see through a prismatic wall using truesight/x-ray vision?
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**Truesight does not help** - a Prismatic Wall is an Abjuration, not an Illusion, and neither involves the Ethereal plane nor shapeshifting.

**X-ray vision is less clear** - Prismatic Wall is defined as one inch thick, which definitely fits within the realm of X-ray vision. However, X-ray vision states "solid objects", which I'd argue a Prismatic Wall isn't, being defined as "a shimmering, multicolored plane of light ". As Prismatic Wall is a 9th level spell, so I'd tend to argue in favor of it doing more rather than less.

However, I'd say the rules are unclear enough that **a DM ruling is required**. And **Rule 0** is always a thing - if the DM wants Vecna, one of the top BBEGs in D&D, to be able to see through something, then Vecna definitely can.
RAW, vague.
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True sight and x-ray vision could either be *argued* to see through *Prismatic Wall* depending on various definitions of light, matter, ethereal, etc. However, D&D 5e is not a physics simulator. Neither *explicitly* states they see through 'planes of shimmering light' or w/e, yet they both talk about seeing through all kinds of stuff, so it's basically an argument either way.

Whenever there's an argument about anything in D&D, it comes down to the DM's decision. That's in large part *why* you have a DM (as well as to apply structure and motivation to the story). What a DM decides is reasonable in that situation is up to the DM and their table's expectations, but,

*Should* Vecna be able to see through his Prismatic Wall?
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Yes.

He is Vecna.