According to a post on NeoGAF, an old Game Boy Advance Mario Kart tech demo has been found that was called MarioKart XXL. The post says the tech demo was produced in 2004 by Denaris Entertainment, and their website listed it among their credentials in the Demos section. You can see it on this archived page. At the time, no one really knew what MarioKart XXL was though.
The demo looks quite different from GBA’s Mario Kart: Super Circuit, in that it shows two Mode 7 layers being rendered at the same time as he drives around the race track. You can see this pretty well in the screenshot below, where we see a second track underneath the one he is driving on.
There is some video footage of the MarioKart XXL tech demo in action, too. You can see it below. In it, he demonstrates driving around the course, zooming the camera in and out, and falling off onto the lower track. The two tracks are not connected by ramps or anything. The grassy-edged paved track is just floating in the air above the beach track. There are coins scattered about on the road, but nothing happens when you run over them and walls don’t stop you either. This is consistent with it being a tech demo though. You wouldn’t expect it to be like a fully featured game.
It is also possible that it could be fake. Some forum-goers on the previously mentioned NeoGAF thread have pointed out that in the video you can see that the tech demo is on a Game Boy Color cartridge when he inserts it into the Game Boy player on his Platinum GameCube. This does not necessarily make it fake, as the insides of a Game Boy Advance cartridge could probably fit in a Game Boy Color one since the older cartridges were larger anyway. If it is fake, I think it would take a fairly advanced ROM hacker to have made it. Whether or not the MarioKart XXL tech demo is fake or not, it is interesting to look at.
