One modder shows how to hook a GameCube controller up to your 3DS for $12

You have to know what you’re doing though

One of the only problems I had with Super Smash Bros. for the 3DS was using the Circle Pad for a prolonged use of time. I actually got used to using the portable’s controls over time, but the pad itself wears on my thumb.

If you have $12 and a lot of technical know-how though, you can mod your 3DS to accept a GameCube controller input. Modder DekuNukem (haha, love it) has explained exactly what parts you need, where you can get them, and how to craft the mod yourself.

Again, just keep in mind that this could screw up your unit if you aren’t careful.

GameCube controller adaptor sample modification [Imgur.com]