I wanted to show someone what Black MIDI was so I started watching some to find a good one that was a nice balance between blackness and sound. I listen to this one, and it didn't stand out to me too particularly much, but it was when I first saw a download button. I downloaded this 222,000 note midi file, expecting it to be absolutely massive, but it was only 1.7 MB. I then threw it into Ableton just for fun so i could see if it would break it and ableton never even went above 10% cpu usage. After listening to the individual parts, I decided it would be cool to change the sounds to some synths. There was a total of 19 parts, so I didn't change all of them to synths, because about half of the tracks just had an occasional line or mashing of notes, those stayed as piano, but the rest of the main melody, harmony, and base I put on synths.
In the end though, I this song isn't that remarkable, it just happened to be the one I chose to download. The best Black Midi I've found so far that's the best balance between note count, sound clarity, and source song is PI (3.141592 million notes) by TheSuperMarioBros2: https://youtu.be/Ay8vzCHkgEk

Original Black MIDI: https://youtu.be/vQfZ0O-pm4A
Original Song: https://youtu.be/P7dLp2Eb7cg
You can faintly hear this theme towards the beginning-middle: https://youtu.be/UFugieKYIH4