Super Mario 64/Super Mario FX

Super Mario FX is the rumored earliest version of Super Mario 64, originally developed for the Super Nintendo Entertainment System using the powerful Super FX chip, used in games such as Star Fox, F-ZERO and Yoshi's Island. Given that it would predate any known build of Super Mario 64, the elusive Super Mario FX should've been in development in around 1993.

While there is no concrete evidence of Super Mario FX's existence, Miyamoto has gone on saying that he thought about creating a three-dimensional Mario game during the development of Star Fox. This has led to the assumption that a Mario game using the Super FX chip could've been in the works for the Super Nintendo, before the existence of the Ultra 64.