What spells or class abilities can prevent possession by a Ghost?

Question

What spells or class abilities can prevent multiple Ghosts from possessing a character?

To set the scene:

You find yourself drifting on a raft and can't believe your luck as you come across a rock formation with a an abandoned ship. You make your way onto the rocks to check out the ship. Suddenly you find that you are surrounded by unfriendly Ghosts. You have heard they can possess people and try to quickly think about what you can spell or class feature you can use to prevent being possessed by one.

Class abilities that could prevent approach or possession altogether:

• a Cleric's Turn Undead
• a Druid's Wildshape

Spells that prevent the Ghost from moving or approaching, like:

• Magic Circle
• Protection from Good and Evil
• Darkness

I am trying to build an extended list of spells and class features, but please do not include strategies such as teleporting to another plane of existence or running into a pitch black cave.

This question is about spells and class abilities.

Possession (Recharge 6). One humanoid that the ghost can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the ghost; the ghost then disappears, and the target is incapacitated and loses control of its body. The ghost now controls the body but doesn't deprive the target of awareness. The ghost can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The possession lasts until the body drops to 0 hit points, the ghost ends it as a bonus action, or the ghost is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the ghost reappears in an unoccupied space within 5 feet of the body. The target is immune to this ghost's Possession for 24 hours after succeeding on the saving throw or after the possession ends. (MM p.147)

Answer 1

One spell exists specifically for this, Protection from Evil and Good. Here's the relevant part of its rules (emphasis added):

Until the spell ends, one willing creature you touch is protected against certain types of creatures: aberrations, celestials, elementals, fey, fiends, and undead.

The protection grants several benefits. [...] The target also can't be charmed, frightened, or possessed by them.

Answer 2

Polymorph/Wild Shape

Since Possession requires a humanoid, using polymorph or wild shape to change into a beast or other non-humanoid creature will prevent the Ghost from being able to possess than creature.

While it will not force a Ghost out of a possessed creature, Polymorph can also be used to encourage the Ghost to voluntarily end the possession. The creature that was possessed would then have immunity to that Ghost's possession for 24 hours.

Blindness/Darkness

Possession requires that the ghost be able to see the humanoid to possess it. The ghost normally does not have True Sight or a condition immunity to Blindness. Creating a zone of magical Darkness or blinding the ghost, ie with Blindness/Deafness, will also prevent possession.

Force Cage/Wall of Force

Both of these spells extend into the Ethereal Plane and prevent the Ghost from going through them. These can be used to prevent the Ghost from getting near you. Of particular note, Force Cage can prevent the Ghost from being able to enter the Ethereal Plane as well.

A creature inside the cage can't leave it by nonmagical means. If the creature tries to use teleportation or interplanar travel to leave the cage, it must first make a Charisma saving throw. On a success, the creature can use the magic. On a failure, the creature can't exit the cage and wastes the use of the spell or effect. The cage also extends into the Etherla Plane, blocking ethereal travel.

Banishment?

The Banishment spell has the potential to end the encounter if the DM is nice. Ghosts are native to the Ethereal plane and thus would be shunted back there if the spell is successful. However, Ghosts can freely travel between the Ethereal and Material planes. Since Banishment does not specify where on the native plane the banished creature is sent to, so it is up to the DM whether the Ghost is within vicinity or not. If the DM is nice, the Ghost does not travel back to the encounter.

Answer 3

Thematic Spells

There are a few ways to achieve this, but first let's focus on spells that actually do mention possession:

• Protection from Evil and Good
  1st level, Casting time 1 action, Duration 10 minutes (concentration)
  Targets one creature and protects it for the duration.
• Magic Circle
  3rd level, Casting time 1 minute, Duration 1 hour
  Targets a small area, barring undead (among others) from entering and protecting those inside against possession. Can be reversed so it barrs undead from leaving and protecting those outside against possession by those inside the circle.
• Hallow
  5th level, Casting time 24 hours, Duration until dispelled
  Targets a rather large area, barring undead (among others) from entering and protecting those inside against possession.

Conditional Spells

There are obviously many ways that prevent possession by means of denying the ghost one or more conditions: in order for possession to work the ghost needs to see its target, needs to be within 5ft, the target has to fail a wisdom save, and there might be other creative ways to protect you, but trying to list them all here would be out of scope. Here are a few examples for each of these categories:

You can stop the ghost from getting close:

• Wall of Force
• Otiluke's resilient sphere
• Forcecage

There is a plethora of ways to prevent the ghost from seeing you:

• Invisibility
• Darkness
• Blindness/Deafness

You can bolster your wisdom saves:

• Bless
• Ceremony
• Warding Bond
• Beacon of Hope
• Motivational Speech