June 23, 1996
In the Mout Rushmore stage, President Washington's face is replaced with Mario's. When shot it changes to Wario's.
March 25, 2011
During the "Three-Minute Glide" Mission, if the player flies through a small village, sounds from Super Mario Bros. can be heard from one of the houses, supposedly being played by someone. After a few notes of the main theme Mario can be heard jumping and then dying, followed by the game over theme.
Copyrights for both series are held by Nintendo.