This is an NPC, or a non-player character.
The Mind Ghost is a ghost introduced during the B.O.O. Update. Upon coming into contact with a player, the player would receive the "Mind Control" mod which will change the controls of the player (pressing right will move left and vice versa).
- Wearing a Foil Hat will make the player unaffected by the ghost.
- Mind Ghosts can sometimes revert to a Ghost.