What a banger!
So many good things to say:
Firstly, the theme is super catchy, joyful and bouncy on first listen when the organ isn't there yet. In the second passage of the theme, the organ kicks in and you surprise us with a spooky, subtle arrangement (diminished notes and tritones).
The transition to the bass solo at 0'51" is fan-ta-stic! The organ intensifies on a final chord and bam! the bass plays a great riff!
The theme returns, but with a tempo divided by 2, reviving the music.
What mastery!
Obviously it fits perfectly with the theme and I could see your music for an RPG boss.
Great Blue Lava as usual