id software sent a PC demo of Super Mario Bros. 3 to Nintendo hoping to gain authorization to make an official port. Nintendo was impressed but declined, deciding to stick to their own platforms. The demo was based on a test they named 'Dangerous Dave in "Copyright Infringement"', which was a playable recreation of World 1-1 with Mario's sprite replaced by John Romero's Dangerous Dave character.
Contributed by Funland47