There are billions of souls out in the world. Some spirits are good, and are looking to become reborn into this world. Sometimes, that doesn't always happen, and they look for residence inside animals, or even dolls. Yes, dolls.
Sometimes spirits develop into malevolent creatures. Remember that time you got yelled at for spilling your cup of fruit punch? It never once occurred to you that it could have been your doll. Or your action figure if you were a boy that didn't have dolls.
But think back to the moment you got blamed for something you didn't do, or something you couldn't recall doing. Was your doll or action figure lying somewhere nearby?
As people live in abodes like houses or apartments, spirits are trying to do the same.