Mario Circuit is a brawl stage in the Wii game, Super Smash Bros. Brawl. It also reappears in Super Smash Bros. for Wii U. Although it shares the name of the tracks in Mario Kart, it shows no resemblance to any of them. In fact, it looks more similar to Luigi Circuit on Mario Kart Wii than any other Mario Circuits. It probably takes its form from Figure-8 Circuit in Mario Kart DS.
As with the other Super Smash Bros. Brawl stages, Mario Circuit is not really a race course. It is two dimensional. Over the bottom section of track, There is two ramps with a floating platform, allowing fighters to go on the upper section.
Throughout the course, Shy Guys driving in different colored karts drive constantly through the track, damaging any players who are in the way. They travel on the bottom portion and top. On the bottom section, you can see the Shy Guys approaching around the loop, so you have plenty of time to move before they recklessly run you over. But on the upper track, they love what the do, you have to be more alert, as you cannot see them coming in. You can attack the Shy Guys to make them spin off the track (Ha...revenge for all the times they ran you over!).
In the background, a stadium similar to the one in Luigi Circuit can be seen filled with bystanders, and a map layout screen depicts the track being in a figure 8 shape, and it also shows the trajectory of the Shy Guys. There is also a sign that says Mario Circuit. Just so you don't forget the name, I guess.