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According to video Game developer Yukio Futatsugi, his tabletop board game Machi Koro was originally going to be a digital board game available on the 3DS, but Nintendo encouraged Futatsugi and his company Grounding to go physical with it instead.

"My company has made a lot of board games, and Nintendo has told me that our games are interesting. Machikoro was supposed to be on 3DS, but the idea didn’t become a reality because it wouldn’t sell on 3DS, and so Nintendo suggested, 'Hey, Grounding, why don’t you manufacture this as a physical board game, I’m sure it will sell really well!' and that’s how Grounding came to become a board game creator."
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Attachment In the Japanese and American versions of the 3DS' "StreetPass Mii Plaza", when attempting to purchase a DLC from a rabbit but then declining to buy it will cause the rabbit to depressively say "Oh, I see...". However, the European version removed the rabbit's depressed response and replaced it with a more neutral "Fair enough!", instead.

This was done to bring it in line with European laws put in place to prevent manipulating children into purchases; "Games should not include practices that are aggressive, or which otherwise have the potential to exploit a child's inherent inexperience, vulnerability or credulity or to place undue influence or pressure on a child to make a purchase."
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Holding the start + select buttons while booting an original Nintendo DS cartridge will load the game in its native resolution, rather than stretching it.
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In 2012 the Louvre museum in Paris, France, started offering 3DS museum guides. The purchase of the hardware was sponsored by Korean Air, and all the museum guides are branded with the airline's logo.
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Attachment Placing the AR Card on a colored surface during the AR Free Fishing game (available from the AR Arcade for 1 Play Coin) yields different effects based on the color. For instance, a blue background will display sardines, a green one will show green Koopa shells, and the red contains jumping Cheep Cheeps.
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Making noise into the microphone while on the system settings screen will cause the icons to spin around the wrench. While doing this, the wifi helper icon can be seen on the back of the internet icon.
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Attachment In the 3DS Sound app, when playing a sound file, switching to the Game & Watch Soccer background and pressing any button will allow you to take control and play the game.
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If you blow into the mic while highlighting a 3DS application, the icon will spin around faster.
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