Rarest video game ever made

Oh, oops. Thats what I get for not keeping up on my Sega history, lol.

 

Air raid on the Atari 2600 is the holy grail of Videogaming!

 

The problem with your question is the collector. When only a few copies are known to exist then many collectors automatically consider it a "prototype" or "variation". When pushed for an answer as to why the number that exists is sometimes given as the reason. One simply can't allow for these games to count as games if you already have what you consider a complete collection.

So the question then really becomes how rare is a game ALLOWED to be and still be considered a game?

The NES AGCI version of Wally Bear was offered for sale directly from the company in a single issue of USA and in book written for overprotective parents looking for kid safe games. One copy does exist but because there is only one it is considered a prototype. Same situation with the NES Sharedata Chiller cartridge. There are more of these perhaps as many as 10-20 in collector's hands but again not enough for many collectors to count it as a separate release. Many NES collectors don't count the NWC cartridge and others take it a step further and consider Stadium Events a variation. Then others take it even further and discount all of these AND every unlicensed game.