John Romero, co-founder of developer id Software, uploaded footage of his PC port of Super Mario Bros. 3. The video above shows a demo of the Nintendo game produced by future members of the id Software team in 1990, including Romero and co-founder John Carmack, which they later sent to the Mario makers themselves.
Known then as IFD (Ideas from the Deep), the team's take on Mario's classic NES adventure isn't the most faithful recreation aesthetically, but gameplay-wise, it's an impressive adaptation of Nintendo's side-scrolling formula.
Nintendo turned down id Software's proposed port, and the team went on to develop Commander Keen instead. It's the anniversary of that game that prompted Romero to share the storied Mario demo today.
https://vimeo.com/148909578
Pretty cool to see. In their version, the Super Leaf is an absolute game-breaker, though.