You know for only having one day to do this, it turned out pretty well! It fits the boss battle theme super clearly, and the instrumentation sounds great. The transition from the beginning into a faster, more guitar-led part is very natural and everything just works, you know? I wouldn't say this song is super Halloweeny but without a doubt it fits.
Great job, hope to see you again! Thank you for completing something despite being so busy with life. I feel you there.