Super Mario Bros. 3 is the first Platform Game to be able to scroll in every direction, including diagonally. Previous Platform Games were limited to straight up-and-down or straight left-to-right.
Author Phobia: Chain Chomps came from an experience Shigeru Miyamoto had as a child, when a dog chased after him as he approached but stopped just inches from him because the dog was tied to a stake.
Bad Export for You: Because the e-Reader flopped in North America, half of the Super Mario Advance 4 cards never made it out of Japan, which left "World-e" incomplete with only one of the mini-game houses open and a rather empty e-Coin castle. All missing levels are available for the Wii UVirtual Console release, though.
Late Export for You: The international release of the game was delayed by over a year due to a ROM chip shortage affecting the entire electronics industry as well Nintendo wanting more breathing room between Mario games, since they had released the Dolled Up version of Super Mario Bros. 2 outside of Japan in 1988, shortly before Mario 3's Japanese release.
No Export for You: North America and Australia didn't receive all of the Super Mario Advance 4 e-Reader levels until its Wii U Virtual Console release, and Europe didn't receive any of them until then.
According to Nintendo Power Volume 10, a power-up where Mario transformed into a centaur was planned.
The NES ROMs contain a bunch of unused and unfinished content, such as entire levels, enemy variants, miscellaneous graphics, different types of mini-games apparently hosted by friendly Koopa Troopas and Hammer Bros., and more.
In addition to the extra World-e content in the Japanese version of Super Mario Advance 4, a lot more had seemingly been planned, as evidenced by the large amounts of unused content on the ROM and the fact that the world's castle, which displays the e-coins located in each of the World-e levels, was originally planned to have three floors, each with a full length e-coin gallery.
id Software created a demo as proof-of concept for their proposed DOS port of the game. While Nintendo of Japan was impressed, they declined as they had no interest in releasing games outside of their own platform. id instead used the technology to create Commander Keen.