Who has ever heard of Kirby Mario Brothers?
It was a Super Mario Bros. 1 hack created in 2003 by some Japanese user named Mikamari. The copyright on the title screen reads "(c) 2003 MIKACHU."
It is programmed as a 1-player game only. Its theme music when you begin a game is the SMB1 underwater theme (normal version). You go down two pipes before you reach the end of the game, picking up the so-called Warp Star.
See it at:
http://www.youtube.com/watch?v=TCJ1vU9WRpY
~Ben