E-Reader

The e-Reader was a card-powered Game Boy Advance add-on that let users scan dot codes to play classic NES games, mini-games in Mario Party-e, get info and play mini-games from Pokémon-e cards, and access some fun stuff in various Game Boy Advance and GameCube games.

e-Readers came bundled with two packs: a "sample pack" of Manhole-e, an Animal Crossing-e card, and three Pokémon-e cards (Machop, Machoke, and Machamp); and a classic NES game of either Donkey Kong Jr. or Pinball.

Unfortunately, the e-Reader failed in the US, resulting in a planned line of Game & Watch games to be shelved (only Manhole-e was ever released, as mentioned above). That said, it did flourish in Japan, being supported until the end of the GBA's lifespan. Europe never even got the thing.

''Scan. Dot. Code.''

Unused Music
There are tons of unused songs within the BIOS, several of which are used for Animal Crossing cards, Mario Party mini-games, and Pokémon cards.

GameShark code (where "????" is the song number) will play any song anywhere.