Nintendo's e-Reader peripheral for the Game Boy Advance always seemed like a solution in search of a problem, but despite the add-on's poor performance in the market, a few interesting things were done with it.  Super Mario Advance 4's extra content is well documented, but SMA4 isn't the only major game to feature intriguing bonus content unlocked by scanning special cards.  2004's Mario vs Donkey Kong also featured its own e-World of extra levels, although you wouldn't necessarily know it.  The content was buried deep and with the exception of a limited release of the e-Reader cards in the Japanese market as part of a promotional contest; the mode was never accessible in the North America version, while it was removed entirely from the European release.  While only five cards were released, there's space for twelve levels in e-World.   Leave it to e-Reader enthusiasts to do some digging and discover how to access all of the seemingly lost data through emulation and a little hacking.  Check out five of the bonus e-World challenges in these videos provided by eddine67 on YouTube.