So, my DM is doing a pvp tourney and I am fighting a Mage (5th level). I am a Shadow Monk and also 5th level. What happened is that in the middle of the fight, the Mage cast Phantasmal Force on me. I failed.

The illusion was of a corridor with one fireball coming from one side, and I, logically thinking, ran away from the fireball and ended up outside the Arena, effectively losing.

The corridor was "infinite" because as I walked the corridor also moved and depth and etc changed to look an infinite corridor. So my question is, this is right? Can the illusion "move" with me? If so, wouldn't allow the "effective" area of effect to be way bigger?


The illusion cannot move from its space

First, the illusion created by phantasmal force, while "rooted" in a creature's mind, has a specific location in real space. This is evidenced by the clause

the phantasm can deal 1d6 psychic damage to the target if it is in the phantasm's area or within 5 feet of the phantasm

If the phantasm did not occupy a specific, well-defined area, then this clause would be meaningless.

Second, illusions which can move from their space explicitly say they can. Spells such as silent image and major image have explicit clauses which allow the illusion to move, with precise definitions of how the illusions can move. (Admittedly, those spells also include the clause that "the image appears at a spot you can see within range".) On the other hand, minor illusion and programmed illusion cannot move from their predefined areas.

If the area occupied by the phantasm were allowed to move, the spell would specify how it could move. It would give the phantasm a speed, or provide some kind of condition for its movement. If you assume there is no limit on how the phantasm can move, then the previous clause specifying that the phantasm can only deal damage to a creature inside or adjacent to the phantasm would be useless, because you could just declare that the phantasm moves into the creature.

Based on the phantasm explicitly occupying an area, having no conditions specifying movement, and the issues which arise if you do assume the phantasm can move, I conclude that the illusion created by phantasmal force cannot move from its space.


Yes, and no

So there is a slight problem with the interpretation, but the end result could be the same.

Per the description,

On a failed save, you create a phantasmal object, creature, or other visible phenomenon of your choice that is no larger than a 10-foot cube and that is perceivable only to the target for the duration.

So the image could not be of an "infinite" hallway, merely 10 ft of hallway. However, the image can adjust as needed...

While a target is affected by the spell, the target treats the phantasm as if it were real. The target rationalizes any illogical outcomes from interacting with the phantasm

So the image could be of a 10 ft hallway, with a fireball going off at one end. But as you race to the far end, walls and ceiling keep attaching themselves meaning that as you run the corridor builds around you with the fireball in pursuit. Think of how Magneto pulls in metal plates to form a walkway as he strides.

So the initial description of "infinite hallway" would fail/not be allowed; it is possible to describe the illusion that keeps up with a moving target.

An example given in the description is:

For example, a target attempting to walk across a phantasmal bridge that spans a chasm falls once it steps onto the bridge. If the target survives the fall, it still believes that the bridge exists and comes up with some other explanation for its fall - it was pushed, it slipped, or a strong wind might have knocked it off.

So the person under the spell fell, but even though they are presumably no longer inside the spell range, the illusion still holds true in their mind.

  • 1
    \$\begingroup\$ The latter example does not actually indicate that the illusion can move. The illusion is of a bridge, and the bridge hasn't moved. \$\endgroup\$ – BBeast Nov 26 '20 at 4:27

The illusion must be no larger than 10 feet a side - but can move with the target

The spell description (emphasis mine) requires that the created phantasm must be of a size no larger than 10 feet a side, thus, a corridor cannot look "infinite":

You craft an illusion that takes root in the mind of a creature that you can see within range. The target must make an Intelligence saving throw. On a failed save, you create a phantasmal object, creature, or other visible phenomenon of your choice that is no larger than a 10-foot cube

That aside, you ask Can the illusion "move" with me? This community resoundingly agrees that a phantasmal creature created with Phantasmal Force indeed can move wherever the target goes (assuming the thing created can move). The accepted answer relies on the fact that the spell "targets the creature not an area or point in space" as well as the following Jeremy Crawford tweet (emphasis as in the answer):

Q: Can be the effect of phantasmal force a bag on the target's head which is moving with the target?

A: Yes, assuming the illusory bag can fit in a 10-foot cube.

If we instead consider a moving corridor that is no longer than 10 feet, nothing in the spell description differentiates between a phantasmal object and phantasmal creature.

RAW and RAI, the target should treat the phantasm as if it was a real moving corridor until it might succeed on an Investigation check. That is even despite the target might not have heard about moving corridors before.

That brings forth the question: What would prompt an Intelligence(investigation) check into an illusion? For which the accepted answer (emphasis mine) outlines the two parts of the spell description that makes Phantasmal Force more difficult to reveal as an illusion than most other illusion spells, i.e. enabling that moving corridors and other extremely creative phantasms can be just as effective as more mundane ones (instead, the spell is balanced out by only being able to affect a single creature and requiring a failed Intelligence saving throw before taking place at all - contrary to Minor Illusion, Disguise Self, Silent Image, Major Image etc.):

From the DM to the players, the way they present the illusion is the way it works (mostly, rules of the spell still apply).


Phantasmal Force

This is a special case, mainly because of two particular things:

  1. While a target is affected by the spell, the target treats the phantasm as if it were real.
  2. The target rationalizes any illogical outcomes from interacting with the phantasm.

If we consider the initial save roll as failed, there is very little that the affected target can do for itself. Number 1 take care of things like thinking it is to odd for it to exist or to be real. Number 2 is particular problematic, since it make any interaction feel real and in order no matter how illogical the reaction or action was. But, there is a solution to this problem, third parties. Since any third party won't see what the affected creature sees, it is very easy for them to connect the dots and establish that something is very wrong with him. They can yell it's in your head or it's an illusion, they can ask what is wrong and latter say there is nothing there or the like. In that case, the affected target have a reason to suspect that it might not be real and act accordingly.


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