Nice work! I like your take on hip-hop and spookiness. Great use of ambiance to give some interesting textures. The intro works really well as some kind of intro to the boss or cutscene as you mentioned in the description.
I think the piece starts dark but it does take a while before I get a Halloween-vibe. The theremin sound-like voice that appears helps a lot with the Halloween theme. I like the idea of the scream but for me personally, it's a bit too loud/too far in front of the mix, maybe try to blend it a bit more with the rest. The calm part sounds very good and interesting, I love how it gives space to let the listener focus on the ambiance/textural sounds and the great use of stereo. I do think that there could have been an opportunity to expand the phase 2 section. For me, phase 1 and phase 2 seem very similar in terms of energy. I think it works very well in this kind of beat-based genre (though I'm by no means an expert) but I do wonder if it could be possible to give a bit more variation. Either on the melody, like adding a second more melodic voice/counter melody that is more prominent. Or, focus more on the beat aspect and give more variations/fills. It works great as it is now and I like it a lot, was just interested in what would happen if you were to develop one of those aspects to its maximum.
Well done and looking forward to hearing more from you!