Yay thanks so much for your feedback!
I still struggle on how to make a good tutorial for this kind of mechanic, I did try to have a tutorial button under the player but its not obvious enough when I watch the streams. I also thought of making the jumps and dash less effectively off-beat, but then the level design would need much more thinking than not executing the action. Will definitely think more about that. I also just have a patch to make players more powerful thanks to your feedback: kill enemies by contact. This game satisfies my will to make a metroidvania but I don't think I will make another one for a game jam haha.
Game-design wise, I get you on the rule of thumb. I didnt have enough time to design all the rooms for that purpose so I squeezed them all in. Would definitely enlarge the world for practicing rooms if I work more on this. Saxophone was for 2 powerups because they are both jumps, but also Im afraid players get overwhelmed with too many tracks to listen. I will surely revisit 140 for some more design choices.
I also hear you on the graphical representation of the black thingy, enemies and other things in the game, just poor design choices. I will improve that and populate the world with more details like vines and all if I work more on it. Thank you very very much for leaving much feedback, it means a lot to me. I see you're busy with your entry in both the Music game jam and Brackeys game jam, good luck with both of your entries!!