Console modding is often popular with retro systems, as those with a tool-kit and some engineering smarts give new life or functionality to ageing hardware. Occasionally someone will mess around with the capabilities of current day systems, for either cosmetic or relatively unharmful reasons, and the results can be rather cool.
As you can see in the image above, YouTuber 4344739's channel has modded a 2DS to be playable with a GameCube controller. It's being partially hidden, but it seems that the charging port at the back has been connected to a GameCube controller extension; quite how the modder has got the hardware to recognise inputs is entirely unclear, especially as the video — at the time of writing — has no description.
The channel's only previous posts are spread out thinly over 7 years, showing video output from a 3DS (two years ago) and DS screens being produced on much larger screens (seven years ago). It seems these projects are simply dalliances, with basic demonstrations then uploaded for the world to see.
This'll never be a legitimate option, so you may as well check out the video below and watch someone playing Super Street Fighter IV 3D Edition with a GameCube controller.
Thanks to Justin for the tip.