A player in my campaign is playing a Unearthed Arcana V3 mystic and has been making use of the Phasing Eye ability. I've been trying to figure out how to curb its use a bit.

The majority of the time it poses no problem and gets used to spy into back rooms or inside containers. When it comes to dungeons though, Phasing Eye gets sent through the entire complex first and there aren't many ways to keep certain areas off limits. I have no problem with it giving the player a chance to scout, it's what the ability was designed to do after all, but it still raises some issues.

  • Time: Scouting can be time consuming. The party is incentivized to send the eye through the whole dungeon, mapping as it goes and then retread the area themselves.
  • Drama: When the whole dungeon is open to perusing it's difficult to implement ambushes, traps or dramatic reveals.
  • DM flexibility: Giving the layout of the dungeon and the position of enemies means things can't be changed on the fly to improve the game. Encounters can't be moved around behind the curtain and it can be weird having to think up an explanation of what any given monster might be doing in its spare time.

Arcane Eye is similar but can be kept in check with well placed physical barriers If I understand Phasing Eye correctly, nothing short of a 30ft. thick wall can hamper its movement.

Mordenkainen's Private Sanctum, as written, only blocks divination spells. I think its pretty reasonable for it to also block Phasing Eye but I'd rather use it sparingly as not every dungeon makes sense to have the spell in effect.

I've considered adding roaming guards who can see invisibility but even if they see the sensor (I think it's unclear if they could or not) they wouldn't be able to destroy or dispel it. The best they could do would be to raise the alarm that an amorphous glowing object has been seen floating around.

Are there alternatives for limiting the ability's use or are there any changes to dungeon design that can be made to better accommodate for it?

There are a handful of other mystics in the campaign. The player is a part of an organisation of other mystics.


4 Answers 4


There are some simple things you can consider without taking away something the character has invested a lot of resources into.

We need to look at the text of the ability to really see what its limits are:

Wandering Eye (6 psi; conc., 1 hr.). As an action, you create a psychic sensor within 60 feet of you. The sensor lasts until your concentration ends. The sensor is invisible and hovers in the air. You mentally receive visual information from it, which has normal vision and darkvision with a range of 60 feet. The sensor can look in all directions. As an action, you can move the sensor up to 30 feet in any direction. There is no limit to how far away from you the eye can move, but it can’t enter another plane of existence. A solid barrier blocks the eye’s movement, but the eye can pass through an opening as small as 1 inch in diameter.

Phasing Eye (7 psi; conc., 1 hr.). As Wandering Eye above, except the eye can move through solid objects but can’t end its movement in one. If it does so, the effect immediately ends.

Speed of mapping and exploring

The eye, as written lasts for an hour and can travel at 30ft per round. That speed is equivalent to 300ft per minute. So, travelling at breakneck speed and not spending any time to look in detail at any room or hallway, it can cover an impressive 18,000 ft in an hour. Some of this will be spent back tracking to account for dead ends and going into rooms. If we lowball it and say 10% of the movement is spent backtracking. That gives the party an effective mapping capability of 16,200 ft of dungeon floor space.

Now we need to ask you some questions:

  • Does your dungeon level have more than 16,200 ft of floor space? (Note I'm not talking about floor area, I'm talking about travel distance)
  • Do your dungeons always connect in a circuit? (for example one level may have two unconnected sides that branch from the entryway, this would drastically increase the amount of backtracking required)
  • Does your dungeon have random dead end passages that go nowhere? (Even after a seemingly long corridor moving with purpose in a particular direction)
  • Does your dungeon have secret rooms and traps?

If your party wants to examine features of the dungeon through the eye, they will cut their speed even further. At a minimum they will be moving at a slow pace (move 15-30ft, pause to look around and examine details).

Traps, ambushes and secrets

The eye is not a creature, and it is incorporeal, so it won't be able to set off traps just by moving past them.

The eye only has darkvision and normal vision. This means it won't automatically spot secret doors, traps or hidden creatures.

The gloomstalker ranger has an ability they get at 3rd level which is relevant here:

You are also adept at evading creatures that rely on darkvision. While in darkness, you are invisible to any creature that relies on darkvision to see you in that darkness.

So the eye won't see any gloomstalker rangers or monsters with similar abilities.

The eye has no way to interact with the environment other than trying to go through solid objects.

Traps can be placed in any surface, including the roof and walls. Finding is going to be difficult for the eye, unless your party is spending time trying to send the eye through every roof, wall and floor, in which case the eye is travelling significantly slower in the forward direction than it's stated 30ft per round. It's hard to make an adjustment for this, but in a dungeon with 10 ft wide and high corridors checking in this way would easily cut its speed to one quarter speed, or further (depending on how thorough they want to be) just by moving around each square in each direction.

If they try to do a thorough search in this way for traps and secret doors, they run the risk of ending the eyes movement in a solid block of stone, at which point the effect immediately ends.

Enemy positioning

Sure the party will get an idea of where the enemies were at some point during their hour long search, but enemies can move in the same way PCs can.

In your prep for the session, position the monsters in different rooms at different times of day, that way you can move some (but not all) of them to a prearranged place other than where they were originally spotted. Also explicitly have wandering monsters that roam the dungeon.

Things that block divination magic

Unfortunately the Wandering and Phasing Eye are psionic forms of magic as opposed to divination magic. As a result magical effects which block divination magic won't affect the eyes.

The fact these powers are designated as magic does, however, mean that for the purposes of effects like antimagic field, and dispel magic they are (or can be) affected.

  • \$\begingroup\$ Thanks for the answer. Funnily enough the Mystic describes psionics as being magic as it says "Psionics is a special form of magic use, distinct from spellcasting.", although the powers are still school-less. \$\endgroup\$ Commented Jun 14, 2019 at 9:33
  • \$\begingroup\$ @Bobnonymous indeed. I should have been a bit more precise in my wording. For the purposes of things that block divination magic they won't block this because it isn't actually divination magic. \$\endgroup\$
    – illustro
    Commented Jun 14, 2019 at 12:59
  • \$\begingroup\$ When I initally wrote magic I had the subtext of "spell" in my mind \$\endgroup\$
    – illustro
    Commented Jun 14, 2019 at 13:00
  • \$\begingroup\$ updated to be more in line with the precise wording. Is that better? \$\endgroup\$
    – illustro
    Commented Jun 14, 2019 at 13:02

Fog Cloud

The eye in question doesn't have truesight; it merely has darkvision. And darkvision does not have the ability to pierce through lightly obscured terrain or heavy terrain.

A combination trap of Glyph of Warding and a few high level Fog Cloud spells (or homebrew your own high-level variety) can flood the entire dungeon with heavily obscured terrain when your player decides to activate the Phasing Eye ability. While this won't stop the players from determining the layout, this will make the eye automatically fail against detecting traps, and ambushes.

And the excuse to put all these here is pretty simple - it sounds like your players rely on this ability pretty frequently, which means that the dungeon's owner probably heard about this and took precautions.

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    \$\begingroup\$ And on top of that, the entire dungeon is now heavily obscured with no place for the fog to disperse. Fill it with creatures with blindsight/tremorsense :) \$\endgroup\$
    – NotArch
    Commented Jun 11, 2019 at 20:18
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    \$\begingroup\$ Welcome to RPG.SE! Take the tour if you haven't already and see the help center center if you need more guidance. Good Luck and Happy Gaming! \$\endgroup\$
    – Someone_Evil
    Commented Jun 11, 2019 at 20:21
  • \$\begingroup\$ There is an official high level equivalent, it is called guards and wards. Among other effects it fills all corridors with mist. \$\endgroup\$
    – Szega
    Commented Aug 9, 2020 at 13:14

Spells that could block the eye

The description of Wall of Force states :

Nothing can physically pass through the wall.

That first sentence could be understood as preventing the eye from phasing through, although it's arguable that the eye wouldn't physically pass through. This would therefore need a GM call. Also it only lasts 10 minutes and uses concentration.

Moving on we have Tiny Hut which states :

Spells and other magical effects can't extend through the dome or be cast through it.

In the UA document you linked to we can find the following :

Psionics is a special form of magic use, distinct from spellcasting.

So a mystic's Psionic powers would indeed be blocked by the Hut, making eye-phasing through it impossible.

It's not very useful either though, as RAW it can only block off an area 10ft in radius centered on the caster, and lasts 8h.

However, these spells can serve as a base to homebrew better warding magic or traps. For example you could imagine a higher-level tiny hut that wholly encompasses the mad wizard's castle. Now the party has to do the scrying from inside the castle, exposing them to wandering monsters and being discovered.

Dungeon design

A few ideas I've used in my campaigns to limit Arcane Eye abuse that could work in this case (though I haven't had to deal with such extensive eye-scrying), from cheapest to most expensive :

  • Hidden passages : unless they are spending half an hour going through every wall in every room (they can be very big rooms), they will miss part of the dungeon.
  • Magical darkness : the eye only has darkvision, they won't know what's inside the darkness
  • Teleporters : teleporters that only people can use, now the eye is in a dead end.
  • Planar shenanigans : maybe part of the dungeon is on another plane

I would give the eye stats like HP=1. AC=14+INTmod (it is very small so harder to hit.) And use the player's saves for the eye. I would also rule that if the eye get's damaged, then I would give one point of damage to the player and give disadvantage to perception until a long rest. (getting poked in the eye hurts!).

With other phasing effects, if you end your turn in a solid object you gain a 1d6 damage and 2 damage per foot to the nearest open space which you materialize. This feature states that the effect ends immeadiatly. It is safe to reason that any damage from any source will have the same effect. So even a wandering monster could bumb into this invisible eye with a failed save. The eye goes pop!

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    \$\begingroup\$ Do you have any experience using this proposed house rule for Phasing Eye? Bear in mind, this requires 7 power points to bring into creation, how do you reconcile your house rule's proposed fragility with the notable cost to the PCs? \$\endgroup\$ Commented Jun 11, 2019 at 15:28
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    \$\begingroup\$ Hey @Rmfidosa, welcome to the site! Just so you know, this site requires answers to be backed up and supported somehow. "Here's what I would do" isn't very helpful if you haven't tested your solution and can show if and how it works! So, if you have experience with your proposed solutions, please edit it in! See here for more details on what we expect from answers. \$\endgroup\$ Commented Jun 11, 2019 at 15:30
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