Some years ago—never mind how long precisely—I came across this video, where the "Black MIDI" gimmick is that a lot of notes are played at the same time:
And I quite liked it (and the visuals in the last part before the outro still make me want to get a tattoo), and so I downloaded the MIDI file and told my computer to make an MP3 out of it with a nice soundfont so I could listen to it and have it sound better than in that YouTube video. My computer did not like the very large number of notes, and the result is something that does sound nice, but also has a lot of varying slowdown, so the 2:30 original is stretched to 4:49. It's pretty weird. I quite like it.