The original question had to be edited. I would suggest that Muley Graves can be seen as a "graveyard ghost." In one respect, his stubbornness is something of the past. He shows himself to be defiant and resistant to the winds of change that blow past him. Yet, he is ghostly in that Muley cannot impact any change in one way or another. He demands to be a force to be reckoned with. However, his time has passed, akin to the graveyard ghost. Muley's own family has moved on and time will pass him. The fact that he is losing his mind is reflective of this.
In another sense, Muley is a "graveyard ghost" because he can only safeguard the memories in his mind. External reality has no regard for someone like him. Akin to a "graveyard ghost," he patrols and controls that which has no meaning to anyone else. He is tied to his father's land, even though his own family has left him and it. His own memories and conception of self are the only things he patrols. The threat of the bank and bulldozer are always there and will outlast him. The constructions of his own mind are meaningless to the world of land acquisition and movement. For Muley, his world is a "graveyard," a collection of that which has long since passed. He operates as a "ghost," without tangible power. Steinbeck uses this metaphor to describe the cruelty of how time passes individuals, without any regard or care for who they were and what they represented. In this, the metaphor is quite appropriate.