Poltergeists are a subspecies of Ghost.
Unlike ghosts, poltergeists can reproduce. They are less powerful than ghosts, but can kill you. They are dimwitted and prone to mischeif (such as topling furniture, making loud noises, killing pets, etc.). They can turn invisible, fly, and teleport.
They are vunlerable to holy matterial, and (like all haunting spirits besides phantoms) will be destroyed if they leave their haunts. They can be killed (with difficulty) in ordinary ways, but will soon return to life.
Polteirgiests can only breed in haunts inhabited by ghost, phantoms, and shades. When ghosts, phantoms, shades, and poltergeists are united, they can create and expand a chain of haunts connected together.
Society and Culture
Poltergeists usually move in packs. They suffer from an irristable urge to make mischief. They will create all manner of trouble to drive someone insane, and eventually kill them. Poltergeists particularly dislike stern well-mannered people who are riggedly confinned to rules and protocols.
Out of all the haunters; poltergeists get along with phantoms the best. Where ghosts and shades are grim and forboding; phantoms are more enjoyable as far as evil spirits go (though even they can get fed up with the poltergeists' antics).
Poltergeist are miserable cowards. If confronted by someone equal to them in power and/or skill; they will flee, unless they have backup.