Woah, that transition from that harpsichord melody to the main piece was so cool. It almost sounds 'dancing skeleton' like. I think the composition aspect is awesome. I like how the sounds aren't exclusively all instruments, especially the laughing sounds and the synthy theremin thing. The progression through sections flows really nicely.
I think, personally it could fit the 'boss fight' theme a little better, but I love the music. Especially that but at 1:08 with the laughing, it sounds like an amazing intro to a halloween movie. A bit Nightmare before Christmas. Good work mate, sounds good.