Garrett Greenwood built something that would have been every Smash Bros. fan's dream during the Gamecube era: A controller that reacts to button presses with various flashy animations.
So for example when you press Down and B at the same time, the character will blink blue as well as the controller. Likewise when you press Y or X to jump, the controller will flash green. When you do a Down Air with the C-Stick, then it will flash red. And it goes rainbow when you taunt. So all this means that in action it goes through the colours pretty fast and it really looks nice.
The model in the video is designed around Falco's character, but it's game-independent and works with all characters. The first part (via Hackaday) shows all the controller's features and then there's a "How it works" section with a disassembled controller: