Link to Original Source
After the death of his son in Iraq, the seller placed the games up for auction hoping "whoever buys the games will enjoy them as much as my son did!". NWC contained special versions of Super Mario Brothers, Rad Racer and Tetris to be played under a fixed time limit. At least 90 of these copies exist in a grey cartridge and were given out to semi-finalists of the 1990 NWC however only 26 of these cartridges exist in "gold" for the winners and are considered to be the rarest and most valuable NES cartridge released. The game can be clear seen lurking in the bottom left corner of the original auction image."