Okay, so apparently THIS is the true boss theme and the one we’ve been seeing in the trailers is the MINI boss theme.
OMG I love this, I miss Yoko Shimomuras melodramatic insane clown music (I mean that as a positive, she’s my favorite game composer), but this track rules. Everything from 00:40 to 01:35 is so fun and pure M&L RPG charm.
I found a YouTube link in your post. Here are links to the same video on alternative frontends that protect your privacy: