A fellow named Madeon fills us in with a live-performance of a mashup (complete with improv solo!):
It's way more spontaneous than I would have thought! I was imagining a lot of preparation. I have no idea what that thing is, or the slightest idea how it works other than what I can glean from the video. All I know is I want one.
UPDATE: This dude (?) is good:
Apparently he's seventeen years old. Sigh.