Amazing
Like you told, it will perfectly fit in a boss fight but I think taht the ending should not sound like the battle was over : it seems to release the tension and you also can't know that you'll beat the mob in about 2 mins : What I mean is that your song should give the impression of a constant tension.
To get a real impression of a fighting, there must also be a second song in the end of that one when the boss has only a few HP left and becomes stronger : it would need an other loop =)
Hope you'll do this but your current song is excellent though :D
I wish to hear more