Nobody can see a ghost in my setting, but they can see a ghost's actions. Ghosts can move or displace somebody's belonging, push chairs, wardrobes and other objects, create a mess and mischief in a house and even throw knives at living people if they are malicious. Only magicians can sense the presence of a ghost with their sixth sense, ordinary people do not feel the presence of ghosts unless the ghost is doing something with objects. The ghost does not have a hidden humanoid form, it is shapeless. Ghosts can not be touched and nobody knows their location even magicians who feel their presence them do not know where exactly they are located. What do you think of ghosts that are always invisible? Constructive criticism needed.