[[Possession was the WORST, Bakura knew that first hand!]]

There's all sorts of different types, a lot of them the spirits of people who either died with strong emotion or with unfinished business, or who didn't have proper rites done for them. Some of them are vengeful and cause terrible disruptions in the home until they can be put to rest, others, like zashiki-warashi actually bring good luck as long as you treat them well!