It took me quite a bit to actually figure out the mechanics of every playable character, but once I did, it was really fun trying to open the door to Nirvana! I think that having a slightly more clear explanation of which character can do what (the levers and switches aren’t that intuitive compared to the mole and human), and I spent way too much time fiddling with those once I got stuck in the top right area, but a well-made game!
For the piano, try playing (↑, ↑, Z+→, Z+↑) if you’re so inclined :)