Zelda and Mario confirmed for US Animal Crossing
Here is the story, straight from Planet Gamecube...
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As for the new NES games in Animal Crossing, as you may have guessed by now, unlocking them early requires the GameCube Action Replay. This information could be considered a SPOILER, so scroll down if you really want to know which games are left on the disc.
It's been known that both Super Mario Bros. and The Legend of Zelda are both hidden on the Japanese version of Animal Crossing. We can now confirm that both are included in the North American version as well. There's no telling when Nintendo will announce the in-game codes to unlock these treasured classics, but you can get them much earlier with the Action Replay. Datel has already discovered an Action Replay code to unlock Zelda, and they are currently working on one to unlock Mario as well. Remember that once these games are unlocked, you can also download them to your GBA for portable play.