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.
id Software is currently working on a new version of Doom. An alpha version of the 2016 title ran earlier this month.
Update: Romero updated the description for the Super Mario Bros. 3 demo video with more on the port's brief history.
"We worked on this demo for a week, after work, and on the weekend all two days," he wrote.
After it was done, the team sent it to Nintendo of America, which "in turn sent it to Kyoto to the mothership office, and the execs there saw the demo and were really impressed.
"However, they didn't want their intellectual property on anything but their own hardware, so they told us Good Job and You Can't Do This."
Devs Make Mario: Castlevania's Koji Igarashi Makes a Super Mario Maker Level