LOVED this game!! It was so much fun. Having the button switch between the various major scales was a fun musical touch that I adored but I'm not really sure most people will know about it switching if you don't have the player aware of that fact, I only figured it out on accident. Give an NPC to tell the player about it during like a first level/tutorial. A few things though, making the jump be the z button rather than the up arrow, space bar, or W keys was a little...weird and it took a minute to figure out because it was not the norm; same with starting the first level, didn't know I had to hit z to start.
For the gameplay, the movement is pretty good for a game jam but I'm not a pro platformer player so I don't know how to give better feedback on the movement other than, it felt pretty good.
It seems like the enemies don't need to be paid attention to at all though because killing them vs just avoiding them give the player the same result; progression. Maybe adding in a time limit or a score system would make having the enemies useful instead of just, existing. I also think making the enemies/helpful NPC's more clearly visible. I wasn't sure that the C enemy was an enemy until he bit me and same with the first NPC that told me about the higher jumping, I thought he was an enemy so I tried jumping on his head at first to kill him.