Haunted

To be haunted is to be sensitive to spirits and be actively observed by spirits. This typically means hearing the voices of the spirits, feeling phantom tugs or prods in certain directions, or getting premonitions if you tune into your surroundings.
In extreme situations, one who is haunted can be possessed. This is typically a spirit's last resort to get something across, as most understand that possession is not typically welcomed by the living and that the spirit wouldn't be able to get away with it for long before being banished.

Across the Realms

Each realm's culture has different stances on what it means to be "haunted".

OVERWORLD

To be haunted means you have done a disservice to the dead, either while they were living or as they died. If an Overworlder is haunted, they view it as a curse and if anyone finds out, they would shun the person. Overworlders, as a general rule, do not know how to stop being haunted in this way.

NETHER

To be haunted means you have done deeds great enough that your ancestors want to be with you and watch over you. If a Netherborn is haunted, they view it as a sign they are doing the right thing and making their ancestors proud. if anyone were to find out, they would support the person who was haunted, and would try to talk to the spirits if possible.

THE END

To be haunted means you have piqued the interest of the dead, in a way that could be malicious or supportive depending on the entity. If an Enderian is haunted, they view it as a sign that they are on the verge of something big and to be careful moving forward. If anyone were to find out, they would take interest in the haunted person's project.

Mechanics

Players can take the haunted trait at any point, but it will be irreversible once official.
If a character is haunted, they can reach out to the spirits for guidance and advice. They will not inherently know the spirits they are communing with, nor are the spirits compelled to tell the truth, but the character can build rapport over time with offerings or discussions. This connection with the spirits is very important to how agreeable they will be if called upon.
Simply asking or casually interacting with the spirits does not require a saving throw, but does require external communication (ie writing or speech).
Trying to control or harness the spirits is a large challenge, getting increasingly difficult the more demanding the task. If trying to force the spirits to behave a certain way, the player must make a Constitution saving throw, with their relationship with the spirits adding or subtracting a modifier to the overall DC. If the character fails the save, roll a d20. On a Natural 1, the spirits possess you for two rounds (aka 12 seconds). On a Natural 20, the spirits do act against your target, but they choose what they do.
The spirits cannot actively deal damage to anyone, nor communicate in depth with those not haunted. Some examples of what they can do are as follows:

• Clouded Mind: you can call on the spirits to faintly materialize around one target, whipping around them. The target must make a Wisdom saving throw or their next attack will be at disadvantage, as reality is slightly blurred.
• Shrieking Secrets: you can call on the spirits to scream at a target, muddling their hearing with distractions and disarray. The target must make a Constitution saving throw or be deafened for a round. If they succeed, they still hear the spirits but are unaffected, while also understanding one random phrase from the spirits.
• Premonition: the spirits can predict some actions, allowing you to not be surprised while you are conscious. They can give you one piece of information, but are fully able to lie at any point.