From the Super Mario Wiki
Mr. Mover is one of the Duel Boards in Mario Party 3. One of this board's unique features is the conveyor belt at the bottom of the board named Mr. Mover. Every turn, it changes colors from red to blue to red again. Mr. Mover takes players to the right side of the board when red and to the left side of the board when blue. Players have to time their turns carefully if they want to go back to their respective start spaces.