This is really fun! Hopefully you can make this into a full game, I really enjoyed the music and the gameplay was really fun. But some suggestions are to if you were to make this into a longer game it would be cool to have some challenges in the actual levels like complete this level without taking damage or in this certain amount of time, but I had no issues with playing the game. Im not entirely sure with what im going with that idea but hope this helped comment helped and excited to see your future work!\
EDIT: What would've been a nice touch was instead of naming the level "The Grave Warning" it should've been "A Grave Warning" just a cool touch :P