From the Super Mario Wiki
(Redirected from Old Cheese)
Cheese is one of the several ways Luigi can earn money in Luigi's Mansion. Cheese is placed in rooms rather spontaneously. If Luigi uses his Game Boy Horror and selects the cheese, a Gold Mouse will be triggered. This mouse will then appear whenever Luigi crosses a randomly selected mousehole, which will be announced by a distinct chime. Luigi can suck this mouse up for gold. This cheese appears only in the dark, and resembles a triangular prism with several holes in it.