Updated: Jun 4, 2021
It is the only prototype that exists of the accessory N64 "Secret Screen" published in September 1997 in the magazine "Electronic Gaming Monthly" (EGM).
Sega had an article in the magazine on the same page discussing the Black Belt system which will ultimately be the Dreamcast.The designers and engineers of the Dreamcast having seen the Nintendo 64 screen transformed the concept into a memory card, the VMU (Visual Memory Unit).
The accessory that was to plug under the N64 controller like the vibration kit was the idea of Dane Galden, the inventor of the Game Handler for Nintendo Nes.The engineer had attempted to sell the accessory to Nintendo before being redirected to EA.The idea was to have compatibility between an American football game and the screen.
This prototype had two screens: N64 Play Action Football and N64 Battleground Domination.There is no full game for either, just a selection screen for soccer matches and a world map.They can be seen on the small screen when you plug the cable into the expansion slot at the bottom of an N64 controller, then you can switch screens by pressing the small button.
Dane Galden will ultimately receive nothing from Sega for his innovative idea.It will be the same with Nintendo and the link cable whose idea was to connect a Gameboy to a Gamecube.Have we stolen his ideas?