KC:D seems to not over do anything. So, the mod I'd like is a mod that would, in extremely rare cases, have the ghost of a person you killed haunting the area he or she died in, but only at night. Being in its presence harms you and only you, slightly, as long as you're there. Appropriately creepy visuals and audio are necessary. You cannot fight it and win.
The haunting can be ceased by various acts of various difficulty. A bandit's ghost might be satisfied if you found his corpse, be it bones or a body, and burying it. Somebody you murdered in cold blood might need to be exorcised by a clergy member. That clergy member will want something from you in return such as certain holy objects before the exorcism before it is performed, and afterwards you must do a service for the church or your reputation plummets. Perhaps your food also tends to go rotten a little quicker if you do not perform the service, a little joke from God until you perform the service.