The e-Reader is an add-on device for the Game Boy Advance released in 2002 that can read dot codes on special cards and interpret them into data. Depending on the card, the data may contain either information or some type of minigame. Several complete Nintendo Entertainment System games were also made available on special packs of cards. It took a total of nine or ten dot codes (two per card) to store the data of an NES game.
In 2004, Nintendo discontinued the e-Reader outside of Japan due to low sales. However, it was supported in Japan until the end of the Game Boy Advance's lifespan. As a result, many cards (particularly the new Super Mario Advance 4: Super Mario Bros. 3 levels, a planned series of Game & Watch releases, and a set of bonus levels for Mario vs. Donkey Kong) were never seen elsewhere.
The Mario Kart: Super Circuit website suggested that e-Reader compatibility might have been planned for this game.