Woah! the beginning is so abrupt, but it is a loop so I understand why. The whole song is really loud and sounds very close, but you did “open FL Studio and do whatever” so I understand it's probably not mixed or anything yet.
You may consider putting the instruments on lower octaves to give it a deeper and more ‘bossy’ feeling, but I suppose this depends entirely on the boss you’re writing this for.
Overall this really does feel like a boss theme. For what it is, it's good, I can imagine desperately trying to avoid all those unfair boss attack moves while listening to this.
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