Flight of the Bumblebee
You need a MIDI keyboard and Chrome, Edge, Firefox or Opera on a desktop or laptop. Not Safari, not iPad, because Apple does not support Web MIDI. Full requirements.
The only piece here where the average is the story
Every other page on this site leads with the peak, because for almost every piece the peak is what decides whether you can play it. Flight of the Bumblebee is the exception.
1,310 notes in 1:09. That is 18.8 notes per second averaged over the entire piece, start to finish. Out of all 315 charts in the library, 258 of them never reach 18.8 notes per second even in their busiest 25 seconds. So this piece spends its whole 1:09 at a rate that 82 percent of the library never touches once.
Its peak, 20.9, is only slightly above that average, because there is no let-up to average against. The piano roll shows why: one continuous chromatic ribbon, running the full width, with no gaps.
Short is not easy
At 1:09 it is one of the shortest things on this list, and that is the trap. There is no section to learn separately and no repeat to lean on. The right hand carries 65 percent of the notes as an unbroken semiquaver line, and the difficulty is purely that it never stops.
It also covers a lot of keyboard, F1 to A7, so the hand travels while it does it. That combination, rapid shifting on top of sustained density, is what puts it at tier 5.
Playing it here
Practice mode is not optional on this one. The chart waits for you, so you can take the chromatic run at a quarter of the speed and actually learn the fingering. Then use the speed control and move up in steps.
Flight of the Bumblebee is in the free tier.