To celebrate the 25th anniversary of Commander Keen's release, John Romero has posted a video showing gameplay of a PC demo of Super Mario Bros. 3 developed by Romero, Tom Hall and John Carmack, with the aim of enticing Nintendo into partnering with the studio for a PC release of its smash hit, which arrived in the U.S. in 1990. 

Nintendo declined the partnership, and the project was reborn as an original title -- Commander Keen -- which debuted 25 years ago today. The innovation Carmack and Hall hit onto was getting smooth console-like scrolling working on early PCs, which did not have dedicated hardware for games. 

While the demo was widely known about, footage of it has not been publicly available before now. An earlier version -- Dangerous Dave in Copyright Infringement, developed by Hall and Carmack using a mixture of Super Mario Bros. 3 graphics and the lead character from Romero's prior game, Dangerous Dave -- had already surfaced on YouTube.