After a Ghost possesses an armored character, is it basically limited to a single attack per turn with disadvantage?

Question

The Possession trait of the ghost says:

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.

So, the ghost has no armor or weapon proficiencies, no Extra Attack, and doesn't get spellcasting. The rules on armor proficiency state:

If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can't cast spells.

So basically the Ghost now does everything at a disadvantage if the target was wearing armor, and is pretty useless offensively anyway.

Last session, I was running Hoard of the Dragon Queen, and my PCs entered room 3E in Castle Naerytar, where I replaced one of the Spectres by a higher CR Ghost. I possessed a Paladin. Am I limited to swinging around a spear, once per turn, with disadvantage, until the Paladin is knocked out?

Answer 1

Your analysis of the relevant rules is correct: the ghost is not proficient with armor or weapons and suffers the consequences. However, the ghost is not, as you say, limited to attacking the rest of the party ineffectively. It can be much worse than that.

Are there any traps or hazards near the party which the ghost is aware of? The ghost can make its victim dash toward these and attempt to trigger them, harming their possessed body and possibly endangering their companions. Are there nearby groups of monsters which would be attracted by a commotion? The ghost can make its victim scream bloody murder as it runs off in their direction. Is the ghost now holding something valuable or useful? Time to throw that down the nearest pit. If nothing else, the ghost has its own body available as a target, and presumably has a much better chance of hurting itself than it would a resisting opponent.

When a ghost possesses a creature, the question it should ask is: what would be the worst thing to do right now? Then it should do that thing.

Answer 2

Consider the Motivation of the Ghost

The lore of the ghost, in the Monster Manual, tells us (p.147):

Unfinished Business A ghost yearns to complete some unresolved task from its life. It might seek to avenge its own death, fulfill an oath, or relay a message to a loved one...Others are driven by wickedness or spite, as with a ghost that refuses to rest until every member of a certain family or organization is dead.

The ghost has business to attend to. As you correctly point out, if it possesses a PC and attacks the party, it is going to be pretty ineffective. So why are you having it do that? Ghosts are not designed to be used as challenging combat encounters for the party¹.

If, in the unlikely event that the ghost's own agenda is served by attacking the party, it needn't use possession - its withering touch is going to be more effective than a single, non-proficient attack, especially if its host body is in armor¹.

Why is it possessing?

If possession is not an effective combat tactic, why is the ghost able to possess? Returning to the lore (emphasis mine):

A ghost is the soul of a once-living creature, bound to haunt a specific location, creature, or object that held significance to it in its life.

Ghosts, in their natural form, have great movement capabilities - a fly speed, incorporeal movement, etherealness. Yet for all of this they have an important restriction - they are bound to a specific person, place, or thing and must remain in proximity to it. They cannot leave the area. Thus the primary reason for them to possess a body is to be able to leave the region they are haunting and go somewhere else to complete their affairs - they would generally not be using the body to attack the party.

Alternately, they may already be where they need to be, but be unable to complete a task without a physical body. If they need to get an object out of a closed box, for example - they can reach through the box, but they cannot open it and take the object out without possessing a body. A ghost should be possessing PCs only when doing so allows them to complete their unfinished business, and it is likely that their lack of proficiencies will not be a hindrance there.

You ask:

Am I limited to swinging around a spear, once per turn, with disadvantage, until the Paladin is knocked out?

No, you are most certainly not limited to that. You can have the ghost simply dash off to attend to its own affairs, leaving the party to give chase. You can have the ghost patiently explain to the party that it is going to need the body of the paladin for a bit, and ask for their help. You can have the ghost threaten the party with harm to the paladin's body, or with forcing the paladin to break their Oaths, if the party interferes. You can have the ghost pretend to be the paladin until a more opportune time for it to slink off without drawing their attention. There are plenty of options better than immediately using a non-proficient weapon to attack the party for no reason.

But if you must

An encounter with a ghost will typically be a social challenge, as the party attempts to discover what the ghost wants and then decides whether they are going to help it or not. If for some reason you want to make the ghost a combat encounter, then as you correctly cite, the possession feature doesn't give the ghost access to the host's proficiencies. But nothing prevents the ghost from using its own proficiencies, and the equipment section of the MM says that we can:

Assume that a creature is proficient with its armor, weapons, and tools.

While no armor or weapon proficiencies are listed in the ghost's stat block, we can again look at its lore², where we are told:

A ghost is the soul of a once-living creature...A ghost might not realize that it has died and continue the everyday routine of its life.

Whether it realizes it is dead or not, a ghost remembers its former life. In fact, the reason it is trapped in its ghostly form is that it is uniquely unable to 'forget' its former life, to leave these memories behind and move on to the next stage of its existence. Thus it is entirely reasonable to assume that it retains its own weapon and armor proficiencies from when it was alive. If it is possessing one party member for the express purpose of attacking the others, it should be selecting a party member whose available gear matches its own pre-existing proficiencies, so as to be able to use those proficiencies to the best effect while in its host body and with the gear that the host has.

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¹_{Suggested reading: The Monsters Know What They're Doing. Undead Tactics: Ghosts and Mummies.
Some selected quotes:}

_{A ghost will possess a player character in order to perform physical actions that it can’t perform in its incorporeal state (such as opening a door or a container or retrieving an object), to talk to people to whom it doesn’t want to reveal itself as a ghost, to move outside the place it haunts, and so forth...}

_{In short, ghosts aren’t interested in combat unless it involves killing someone they’re compelled to take revenge against. They’ll fight back with Withering Touch to defend themselves, but as soon as it’s no longer necessary—or they’re hit with damage that truly hurts them, or turned—they’re done.}

2_{While it is unusual to need to refer to a monster's lore in order to effectively run them in combat, it is not unheard of. For example, if the players held an undead or golem underwater in the course of a combat, a DM would need to refer to their lore to realize that they do not need air and the suffocation rules do not apply. That information is not contained in their stat block.}

Answer 3

The ghost lacks all proficiencies of the possessed creature.

The quoted rule from the ghost's stat block confirms that the attacks with the spear are limited to one per turn and done with disadvantage and without proficiency bonus, since it does not have access to any of the target's proficiencies (in particular, weapons and armors) and it can not employ any class features (e.g., Extra attack).

This means that even if the ghost has time to doff the armor¹, the attack with the spear can not include its proficiency bonus, since the ghost is not proficient with this weapon: from the equipment section of the MM:

Assume that a creature is proficient with its armor, weapons, and tools. If you swap them out, you decide whether the creature is proficient with its new equipment.

Hence, the ghost is not proficient with a spear.

Anyway, as a DM you can rule otherwise: for example, if the ghost was a soldier in his life, it could be proficient with simple and martial weapons

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In combat, as dave20 explains in their answer, the ghost can take Actions and Bonus actions that are available to all creatures, and can move. For example, the ghost can make the possessed creature towards a menace (a dangerous terrain, down of a cliff, inside the AoE of a spell).

From a DM perspective, the Possession trait could also be very effective/usueful outside of combat, mainly for plot reasons and/or hooks.

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¹ The time depends on the armor type: see Getting Into and Out of Armor.

Answer 4

A ghost possessing another character is limited to one Action, one Bonus Action, and moving a distance up to the possessed character's speed.

The ghost has the Actions available to the the character its possesses, so long as they do not originate in class features or proficiencies. It also uses the target's statistics, and thus gains its movement speed. The ghost can use that movement speed every turn.

It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The ghost can use a bonus action to end the possession.

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.

Because the ghost does not have Proficiency in armor, it has disadvantage on most types of rolls.

If you wear armor that you lack Proficiency with, you have disadvantage on any ability check, saving throw, or Attack roll that involves Strength or Dexterity, and you can’t cast Spells.

For this ghost to avoid disadvantage on most ability checks, it would need to doff the armor of the target it possesses and only take Actions that do not require proficiencies it lacks.