Unless

def passable?(x, y, d)
    new_x = x + (d == 6 ? 1 : d == 4 ? -1 : 0)
    new_y = y + (d == 2 ? 1 : d == 8 ? -1 : 0)
    unless $game_map.valid?(new_x, new_y)
      return false
    end
    if $DEBUG and Input.press?(Input::CTRL)
      return true
    end
    super
  end