Thanks for the kind words on behalf of myself and PaperTuna.
When it comes to the boss arena, I was aware that it was “hidden” and wanted to somehow indicate to the player which direction to go, but I didn't manage to do it in time (you can see that the islands are terribly empty, which I was going to change :P). In fact, the arena being so low was a quick solution to prevent the player from escaping it (but the truth is that I should have set it up so that the arena was visible when leaving the church, with a jump down to the arena from the side).
As for the music, these were the first songs ever created using DAW (professional music creation tools instead of the simple “press blocks” like BeepBox) by PaperTuna. I think it turned out great.