Can Illusory Walls be created to be transparent one way?

Question

Must an illusory wall be "viewed" from both directions? For example one that is over a door, clearly from one direction the door will look like a wall, but would it not also hide the door from the other side as well? Could it be created so that only one side is an illusion while the other shows reality?

Yes I can see this being an issue of being able to create fantastic sniper blinds if they can work this way.

I should mention that its not for the caster of the spell that its important, but for allies of the caster. Say, guards defending a keep. The wall doesn't look like there are murder holes, but the guards can see through them and still fire.

Answer 1

For most illusions, disbelieving allows you to see through the effect, but this spell explicitly prevents such use. If the caster was familiar with a one-way material, they could create a wall apparently out of that material. It seems unlikely that a caster would have encountered a one-way mirror in most settings. Not to mention a mirror wall would be suspicious in its own right.

In your example, if the wall was not thicker than the recess for the door, you would end up with a door opening into an apparent wall. Very Winchester House. Otherwise, the wall would simply hide the door from both sides

Answer 2

Almost certainly no

The spell specifically provides that Although the caster can see through his illusory wall, other creatures cannot and does not permit the caster to designate any individuals that share his/her exemption from the spell's effects. The spell's description also says that detecting the illusion does not make it disappear and describes the illusion as appearing "absolutely real".

Even if the caster personally demonstrates the illusion to the guards, such that all guards have passed their saves, it still obstructs their line of sight. That won't help.

That leaves you with, for instance, adding a decoration to the illusion of those paintings with eyeholes. I doubt the spell can create complex wall decorations like that. It is restricted to creating fairly bland and uniform-looking things - walls, floors, ceilings, or a similar surface. You can probably make phony wallpaper or carpet that doesn't look out of place, but a decoration on a surface is distinct from the surface itself. I would rule that the spell is not powerful enough to decorate the surface that it makes (so no paintings on the "wall", definitely no mirrors casting reflections, and probably no signs either.)

Answer 3

RAW says no. RAI....maybe?

The spell's text itself clearly states that the illusory wall remains visually solid no matter how often you phase through the wall, so seeing through it is a no-go.

There is one thing you may have to clear up with your DM (or yourself):

Is the inside of the Illusion filled with air or illusory rock?

The text of the spell doesn't state anything about the inside of the illusion. As such it would be up to the DM to rule how deep the illusion goes.

If there's nothing and you can see through the inside of the wall (kind of like glitching into a wall in a video game), 1 Foot of thickness makes the wall reasonably three dimensional to reasonably fit and still hide the front of a humanoid and a carefully placed ranged weapon. Though it would be fairly hard to judge where the wall's face begins (since you cannot see it from inside), so whoever assaults that wall may see the business end of crowssbows (or at the very least see their bolts) darting through the solid wall.

Answer 4

It seems to me that you could create a wall similar to what they use on buses in places, perforated window decals.

It is usually a thin light metal filled with tiny holes that they paint and put over windows (just no windows in this scenario). From a distance it looks almost like a solid wall or at least preventing anything from firing out. But when you are right next (and some lighting conditions) to it it is fairly easy to see through it. So your guards could see outside and fire through it, but the enemy wouldn't really be able to see in.

The enemy may notice an oddity, but wouldn't immediately know and if you made a whole section look like that they wouldn't know which area was deadly without being very observant during the first volley.