Spy vs. Spy IV: Spies in Space (lost build of cancelled PC game sequel based on "MAD" comic strip; existence unconfirmed; mid-late 1980s)
The ending of the C64 version of the third game in the series which the fourth game was supposedly confirmed.
Status: Existence Unconfirmed
Spy vs. Spy IV: Spies in Space is the rumored fourth installment of the Spy vs. Spy computer games based on the popular MAD comic strip by Antonio Prohías.
Spy vs. Spy was a regular comic strip in MAD Magazine. Each edition of the strip involved the 2 titular spies, White Spy and Black Spy, plotting against the other, attempting to outsmart them, usually via comical means. Because of the popularity of the comic, the Spy vs. Spy series had 3 known video games produced for the Commodore 64, as well as a rumored 4th game that was teased at the end of the third game, titled Spy vs. Spy III: Arctic Antics, which was released in 1987. These games were known for having multiple endings involving each spy outwitting the other with usually comical results. However, one specific ending to the third game supposedly teases a 4th installment in the Spy vs. Spy series of video games, where both spies enter rockets blasting into space, with the text "SPIES IN SPACE" on both of them. This ending was removed from later ports of the game for unknown reasons.
Because of the vague nature of the ending, it is unknown if there was actually a 4th game in the series, and even if the 4th installment was worked on at one point, it's unknown how much work on it was done before cancellation. The fact that the ending was removed from later versions of the game, however, implies that at one point the game was in development, but was cancelled.