Contrary to popular belief, Smithy is not the same of the sword that plunges into Bowser's Keep. The sword is called Exor, and it is actually Smithy's means of transportation and way of linking the two universes. Even a commercial promoting the game got the names wrong.
In Booster's Tower, Mario can go through a curtain and come out on the other side looking just like the Mario from Super Mario Bros. This only works once.
When Mario uses the shower in the Marrymore Hotel Suite, while inside he whistles the World 1, Stage 1 music from the original Super Mario Bros.
Bowser has different battle victory animations in the American and Japanese versions.
The last Mario game ever made for the Super Nintendo.