During the end credits level, Mario/Luigi will appear in the background doing a dance that involves swinging their arms from side to side and taking a step in the direction of each swing. This could be a reference to "Do the Mario", the end credits theme to the 1989 animated series "The Super Mario Bros. Super Show!" during which the dance is performed by Mario, portrayed by professional wrestler Lou Albano.
Contributed by MehDeletingLater