Putting the boss scene near the spawn at the beginning is an awesome idea, it puts you to death initially, but it gives me more motivation to discover what ability do I need to get to beat the boss. I also like you don't force the player to find all abilities to beat the boss (so far I probably don't need flying, it just takes a bit more time)
Also I love the art you did, everything in the game scene does match each other, and the combination of the art & music makes me immerse to the world