By traversing, and communicating through the Bond: you can influence a spirit discretely, implanting or reading emotions and ideas without a trace, or assaulting the victim, overwhelming them with emotions or ideas. Known spirits, either through familiarity or knowledge, are far easier to manipulate, and all manipulation leaves a trace or scarring that is unique to each mentalist. Emotions are like fire, they are intense but will quickly go out if not stoked. Strong Mentalists know how to both stoke and smother the fire, as well as how to move the fuel from one emotion to the next. Ideas are permanent--carved into the walls of your head. Strong Mentalists know how to implant the ideas--both long and sort term--they want, and suppress the ones they don’t, covering old thoughts behind layers of new ones. Beware, while it is possible for a skilled mentalist to tell the difference between two peoples ideas, and thus identify implanted thoughts, it is impossible for a mentalist to tell the difference between their own ideas and the ones they have implanted in themselves.
It is not uncommon for Mentalists to fortify their own minds, creating complex mazes, and palaces to hide their thoughts and ideas. Other mentalists attempting to affect them, may find themselves physically navigating these tunnels, and corridors. Additionally, some heroic mentalists have been able to pull others into their minds, trapping them in their own mind jails, where they have full control of the walls. But it is a dangerous thing having another person in your mind.