I adore Possession - it's in my ten favourite cards, because of how much having it in the kingdom completely redefines the game - but it's horribly designed in at least one major respect: it's only fair in 2-player. I refuse to use it in 3+ player games because it emphasises turn order to a ludicrously high extent in a way that no other card, not even something like Tribute or Masquerade, really does.
I would actually argue that Possession is more fair in a 3 or 4 player game than in a two player game. In a 2 player game, whoever gets Possession first has the chance to possess the other player's possession buying turn or even their possession playing turn. So, first possession is a significant advantage.
In a three player game, if I buy the first Possession, I'll be slowing the player to my left from getting a possession and playing it. But, I'm doing nothing about the player to my left. He can then possess me and help the player to my left by stopping me from possessing him. That way, once the player to my left gets a possession thanks to the player from my right, things are balanced out.
In a four player game, some of the imbalance returns. If the two players across from each other get the first two possessions, then the other pair each has a disadvantage because they're getting possessed but can't possess. But, the imbalance is less than in two player because by playing possession, you aren't making it harder for yourself to get possessed. That only comes up in two player.
