I agree this has a horror-esque feel to it in the sense that there is almost a sense of being hunted. This is especially present when the song increases in tempo in the last third of the piece.
One of the problems, as I see it, is there is an inadequate sense of tension to support that "scare" vibe. One suggestion I have is to try messing around with the buildups before the drops so the piece doesn't play like you'd expect it to. In the final third of the piece, you do this a little already, at around 2:16, and again at around 2:36.
Normally in this kind of track repetition isn't something I'd complain about; it could be used in many different ways to support the intention behind the track. However, from my experience, if the mood you are going for is "dark horror", repetition and traditionally expected cues in that piece can be especially detrimental and the intent tends to not be seen as clearly.
I'm curious about the title. Out of curiosity, what were you thinking when you named this track "Darkside"?
Overall, I'd say it's a pretty good piece, considering Dubstep isn't typically associated with horror themes. I just think it needs a bit of work so the mood you are going for is expressed in a way that is seen the way you intended.
I hope you find this review useful. :)
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