Nintendo Campus Challenge 1991 (1990)

Nintendo made this cartridge for a run of 58 campus tournaments across the US, with special versions of Super Mario Bros. 3, Pin-Bot and Dr. Mario played against the clock, and the carts were supposed to be destroyed afterward. One escaped: an employee assigned to destroy it reportedly kept it, then sold it at a garage sale in 2006 after leaving the company. It is described as the only known surviving copy, so its whole legend rests on one cartridge and the short chain of people who have owned it.