Can a ghost enter a Resilient Sphere?

Question

The spell Otiluke's Resilient Sphere says that nothing can pass through it. The spell Wall of Force says that too, but the Wall of Force spell also says that the spell extends into the Ethereal Plane, preventing ethereal travel.

From this, my understanding is that a ghost could move through the sphere but wouldn't be able to damage the creature inside by using it's Etherealness action to move to the Ethereal Plane, then moving to overlap the creature, then using Etherealness to return. Is this correct? Or does something stop the ghost from returning to the Material Plane?

Answer 1

Otiluke's Resilient Sphere blocks the ghost's ethereal travel

Any wall of magical force exists in and blocks movement in both the plane it exists on and the corresponding border ethereal, as described in the DMG's section on the Border Ethereal (emphasis added):

A traveler on the Ethereal Plane is invisible and utterly silent to someone on the overlapped plane, and solid objects on the overlapped plane don’t hamper the movement of a creature in the Border Ethereal. The exceptions are certain magical effects (including anything made of magical force) and living beings.

Otiluke's Resilient Sphere, which is a magic spell, creates "a sphere of shimmering force", which means the sphere's barrier is made of magical force that blocks ethereal travel. Hence, even if the ghost goes into the Ethereal Plane, it is still unable to enter the sphere (or escape it, if is trapped inside).

Incorporeal Movement probably doesn't help the ghost either

In addition to having access to the Ethereal Plane, the ghost also has Incorporeal Movement, which simply lets it pass through most things regardless of what plane it is currently on:

The ghost can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Unfortunately for the ghost, I don't believe a creation of magical force is the same as an object. I don't have an explicit reference for this, but for example, the text of disintegrate lists "object" and "magical force" separately, as if they are considered different things:

The target can be a creature, an object, or a creation of magical force, such as the wall created by wall of force.

Hence, I don't believe that the ghost's Incorporeal Movement is intended to allow the ghost to pass through barriers of magical force.

Answer 2

The ghost cannot enter the sphere from the ethereal plane.

Here is the full spell text for the 4th-level spell Otiluke's resilient sphere (emphasis mine):

A sphere of shimmering force encloses a creature or object of Large size or smaller within range. An unwilling creature must make a Dexterity saving throw. On a failed save, the creature is enclosed for the duration.

Nothing—not physical objects, energy, or other spell effects—can pass through the barrier, in or out, though a creature in the sphere can breathe there. The sphere is immune to all damage, and a creature or object inside can’t be damaged by attacks or effects originating from outside, nor can a creature inside the sphere damage anything outside it.

The sphere is weightless and just large enough to contain the creature or object inside. An enclosed creature can use its action to push against the sphere’s walls and thus roll the sphere at up to half the creature’s speed. Similarly, the globe can be picked up and moved by other creatures.

A disintegrate spell targeting the globe destroys it without harming anything inside it.

As noted, this spell lacks the distinction made in other spells such as the 5th-level wall of force and 7th-level forcecage, in that it does not specify that it extends into the Ethereal Plane. However, the Dungeon Master's Guide states in its section on the Border Ethereal* (DMG page 48, emphasis mine):

A traveler on the Ethereal Plane is invisible and utterly silent to someone on the overlapped plane, and solid objects on the overlapped plane don’t hamper the movement of a creature in the Border Ethereal. The exceptions are certain magical effects (including anything made of magical force) and living beings.

This would indicate that although not explicitly stated, as an effect made of magical force, the barrier does extend into the Border Ethereal. Because the barrier exists on the Ethereal Plane and does not allow anything to pass through, the ghost is not able to access the inside of the sphere through the Ethereal Plane.

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^{*It may be worth noting that this verbiage is only present in the DMG, and does not appear in the PHB/Basic Rules section on the Border Ethereal.}

Answer 3

Yes, a ghost can enter the space enclosed by a resilient sphere.

tl;dr By traveling to the corresponding location in the ethereal plane, then using etherealness, the ghost can come into the prime material plane in the space inside the resilient sphere.

Ghosts can move between prime material and ethereal planes.

Ghosts have ability to move between the prime material plane and the ethereal plane:

Etherealness. The ghost enters the Ethereal Plane from the Material Plane, or vice versa.

Locations correspond between the prime material and the ethereal planes

There is a space inside the sphere that corresponds to a space on the ethereal plane. The ghost can move to that location and then use etherealness to travel to the material plane at that location.

...overlap the Material Plane and the Inner Planes, so that every location on those planes has a corresponding location on the Ethereal Plane.

A ghost can occupy the space of another creature or object.

Resilient sphere encompasses a creature or object, so moving into it requires occupying the same space as the enclosed creature. Ghosts can do this, but it damages them.

Incorporeal Movement. The ghost can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Resilient sphere does not extend into the ethereal plane.

In contrast to wall of force resilient sphere does not state it extends into the ethereal plane.

Some magical effects also extend from the Material Plane into the Border Ethereal, particularly effects that use force energy such as forcecage and wall of force

Answer 4

The Ethereal Plane is like a fourth dimension.

Ottiluke's resilient sphere does not specify that it extends into the Ethereal Plane while wall of force does. Therefore the sphere does not prevent entering by way of the Ethereal Plane.

The Ethereal Plane adds a fourth dimension which can be used for moving around with suitable capabilities (such as the Ghost's Etherealness). Also see this question:

Does the Detect Evil and Good spell see through a Night Hag's Etherealness?

A 3D blockade does not block 4D movement. It is like a 2D blockade (fence) and 3D movement (flying). Therefore the spell does not block Ethereal Plane movement.

The size of the sphere poses a problem, though, which corresponds to the enclosed creature's size.

The sphere is weightless and just large enough to contain the creature or object inside.

Spatial restriction do not normally apply strictly to a ghost since it has the Incorporeal Movement trait, although moving through matter is considered difficult terrain and might cause damage if the ghost ends its turn there. Ottiluke's resilient sphere is very specific in explaining that nothing can move through, therefore it also applies strictly to the ghost. The ghost is medium size which means it could only move into a medium or larger sphere (or a small one with squeezing). PHB p. 191 states that one cannot end one's movement willingly inside another creature and the wording of Incorporeal Movement indicates that this rule applies to the ghost (emphasis added):

The ghost can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

There is no indication that using Etherealness counts as movement therefore, the rule one ending movement does not apply.

Therefore, the ghost can enter the sphere through the Ethereal Plane.