Hey there Liam,
Really enjoyed that Castlevania track! Your samples sound very authentic, also you have agreat understanding of classical harmony (there were certain times I thought you were heading a certain direction but you'd modulate to somewhere I never really expected. Nice!).
I think overall the composition is great, I just think don't be afraid to double some of your instruments with punchier samples, for example:
The melody could be a lot thicker and present (not necessarily louder cos everything is already balanced beautifully), maybe try doubling it with a grittier synth line possibly with some drive.
I like your drum rhythms, yet again they could be punchier, if you don't want to double the drums with new samples then play around with compression (try mid to slow attacks and even slower release times) and drives.
One last tip - this usually works well with electronic music (whether it be EDM, Chiptune, trance, etc etc) in the climactic sections of your songs add a layer of white nise and side chain compress it to either your kick or snare ad adjust attack/release so that it pumps rhythmically with your tune. This really helps lift some mixes imo. Not sure if this tip will work with your track, but it's definitely worth trying. Check out this video for moreinfo on that
Hope that helps!