You can implement this using Layers.

• Create two new layers "Ghost" and "Player".

• Assign the "Ghost" layer to the players who are ghosts.

• Assign the "Player" layer to the players who are not ghosts and to any objects which are not supposed to interact with ghost players.

• Keep anything which is supposed to interact with players and ghosts equally (like walls, trees and terrain) on the already existing "Default" layer.

• Set the layer collision matrix under Edit -> Project Settings -> Physics -> Physics Manager as follows:

  • "Ghost" collides with "Default" but not with "Player" and "Ghost" (unless, of course, you want ghosts to interact with each other)
  • "Player" collides with "Default" and "Player" but not with "Ghost"

You can implement this using Layers.

• Create two new layers "Ghost" and "Player".

• Assign the "Ghost" layer to the players who are ghosts.

• Assign the "Player" layer to the players who are not ghosts and to any other objects which are not supposed to interact with ghost players.

• Keep anything which is supposed to interact with players and ghosts equally (like walls, trees and terrain) on the already existing "Default" layer.

• Set the layer collision matrix under Edit -> Project Settings -> Physics -> Physics Manager as follows:

  • "Ghost" collides with "Default" but not with "Player" and "Ghost" (unless, of course, you want ghosts to interact with each other)
  • "Player" collides with "Default" and "Player" but not with "Ghost"