Under what conditions can a ghost possessing a creature attune to a magic item?

Question

A ghost can possess people ('humanoids'). It can also go onto the Border Ethereal, phasing between two planes of existence. This means its interaction with physical objects varies based on where it has gone plane-wise and who it is 'inside', person-wise.

Attunement requires a very specific process:

Attuning to an item requires a creature to spend a short rest focused on only that item while being in physical contact with it (this can't be the same short rest used to learn the item's properties). This focus can take the form of weapon practice (for a weapon), meditation (for a wondrous item), or some other appropriate activity. If the short rest is interrupted, the attunement attempt fails. Otherwise, at the end of the short rest, the creature gains an intuitive understanding of how to activate any magical properties of the item, including any necessary command words.

It is not clear who is touching things while one is doing Possession. The ghost is using the person 'as a puppet'. By holding a magic knife with a puppet one is NOT touching the knife at all. Yet, if arrested, pointing out 'the magic knife is attuned to the puppet!!' does not help much. After all, possession is 9/10ths of the law.

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Can a ghost attune to a magic item? If so, under what conditions?

Answer 1

It isn't totally clear, so it's up to the DM

The language of the ghost trait Possession really doesn't give us enough information as to who would actually be attuning to an item if a creature is Possessed.

Because of the lack of clarity, this becomes a bit of a thought exercise for the DM. I'm having a hard time coming up with a scenario in which a Ghost would possess a PC and then the DM would be controlling the PC to attune an item.

While it can happen, the situation is created by the DM and needs to be resolved by the DM. I'd also be pretty wary about taking away agency from a player for this long and doing this.

But if you're using this as a means for something else, then if it tells the story and is fun for all, then it's whatever you've done was right.

Answer 2

A ghost is a ghost; it is not the body/host being possessed

The description for the ghost's Possession action states, in part:

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.

Also, the Attunement rules state, in part:

Some magic items require a creature to form a bond with them before their magical properties can be used. This bond is called attunement, and certain items have a prerequisite for it. If the prerequisite is a class, a creature must be a member of that class to attune to the item. (If the class is a spellcasting class, a monster qualifies if it has spell slots and uses that class's spell list.) If the prerequisite is to be a spellcaster, a creature qualifies if it can cast at least one spell using its traits or features, not using a magic item or the like.

So first off, if the item has any prerequisites, it is a no-go. Ghosts do not count as spell casters, nor are they any class. And since the ghost cannot use the host's class features, it is still class-less. So all those magic items are automatically disqualified.

For the rest, the ghost cannot be targeted by spells or effects. As a DM, I would qualify attuning as an effect, as without attunement the item will act as non-magical. Therefore, it stands to reason that an effect has occurred during attunement.

Attunement also requires physical contact. The ghost has control of the body, but it is not the body. If it was the body, then possession would overwrite the hosts Strength score also.

Now, with all that being said:

It's up to the DM

If it's important to the story, then make up a rule.

There is also this phrase from the Adventure League FAQ

The Adventurers League FAQ v9.0 includes the following guidance on magic item attunement:

Attune to a Magic Item by Familiars

Any item attuned to a creature under your control (familiars, beast companions, etc.) counts against both your character’s limit of three attuned items and the character’s permanent Magic Item Limit.

This doesn’t suggest that such creatures can attune to magic items. Whether or not a mindless undead creature, for example, can attune to and utilize a magic item is still subject to DM discretion.