An evil/negative force. Something around you or within you that tempts you to do the wrong thing, to blame others and be naughty. Could be a warning to clean up your act. Devils and demons in dreams are often referring to your own personal demons such as addiction, a bad behavior or attitude, a weakness, etc.
A demon possession suggests that whomever is possessed in the dream is being overwhelmed by an idea, attitude or other influence in waking life…. to the point they no longer seem like themself May be time to bring yourself or the person back to reality.