Finally got around to playing this submission! I love metroidvania/castlevania games, and this game definitely nailed that vibe. Honestly kinda felt like playing Castlevania using only the ricochet ball sub-weapon (Not sure what that is called)
Anyways, fantastic work overall, I felt the art and everything fit the gameboy aesthetic very well. The only minor nitpick I'd give is that the gameplay could be a bit more interesting if it had more to do with the secondary theme, it felt like you guys had a planned gameplay style you wanted to do before knowing the secondary theme, and were like yeah, let's just say this castle is in space.
That said, obviously my lowest points for you goes in the interpretation of the secondary theme, but don't let that bother you, you nailed everything else and it was an enjoyable experience! I hope you finish whatever vision you had for this project, and continue to make games in the future!