Mouse_left you use for the Mousebutton.
I think you mean if you move the mouse the entity should it too. for that you use mouse_force.x and mouse_force.y.

Code:
action my_action()
{	
  while(1)
  {
    my.x += mouse_force.x; 
    my.y += mouse_force.y;
    wait(1);
  }
}