To a point they interact with your saves, quickloading for example, as well as purposefully removing or Destroying UI buttons.
On Pacifist run: Asgore mainly, Undyne to some degree as well.
On Genocide run: pretty much everyone from pacifist run, except the only one you never fought on pacifist.
On Genocide run: pretty much everyone from pacifist run, except the only one you never fought on pacifist.