Alrighty! 'Bout time I finally sat down and put my votes in!
Tremendouz - Really threatening and tense, which is great for a boss encounter. Your piece had a lot of impact in that way, although my only complaint would be that it takes a while to get to the real 'battle' part of the theme, but that doesn't hold it back too much from fitting incredibly well for an intense boss encounter.
LordMev - Love the metal approach, that particular genre lends itself real well to boss encounters! There was a real sinister feel to a lot of your song, which is great for enhancing the threat of the boss.
hslesperance - Definitely get an old RPG feel out of this one. Personally, I feel it lacks some impact as the theme of what is normally an intense battle, but it makes up for it with emotional impact, like there's more of a story here we should focus on.
floflo79 - Love the DOOM feel! This just sounds straight up cool and gets me pumped for an awesome battle with a great demon or something of the like.
sharprainmusic - Straight up, this just sounds so freaking cool. How upbeat your song is works for a boss theme really well, it's great at keeping the head bopping and the blood pumping. I love how the softer orchestral parts make your song a combination of emotional and funky, which both gets me invested and keeps me excited.
Danilo_Ciaffi - There is just so much right with this one. It's intense, it's emotional, it's threatening, there's an nice idea behind it. It's straight up a great piece both as the theme for a boss fight, and for a solemn, story-driven encounter
Avaruussaha - Love the idea of the multi-phase theme for a multi-phase battle (totally not biased by my history with the idea.... ). The guitar riffs were really badass, and overall the song is really intense
Mairiba - I think the start really fits what you wanted here. It feels like the opponent is toying around with me, which just shows to show that they are indeed experienced. The song is a really nice listen, funky as hell, and guitar melody is awesome. And the heavier sections are great at increasing the tension.
Overall, every piece had theirs strengths as boss themes, and the variety made for some great material to listen to. Now, for my votes....
3RD PLACE - sharprainmusic
2ND PLACE - Tremendouz
1ST PLACE - Danilo_Ciaffi
HM - Mairiba