So I was playing around on an nes emulator when I found this game which is a fighting game with MARIO CHARACRTERS!

The opening and all the characters are from super mario cart I have no idea why.

link to the game:
http://www.playnes.net/play/434/Kart_Fighter.html

Some of these characters were made for MUGEN. I remember the weird Peach and Koopa Troopa characters.