Gotta say, I would have NEVER thought of combining a puzzle game with a rhythm game. It's such a unique idea and I'm all for it!! Also, that music has one heck of a groove! Had me bobbin my head the whole time! I love it. The art, which simple, has a very pleasing aesthetic too :)
In terms of this idea of combining puzzles with beats, at the moment, I feel like it's not quite coming together the way you intended. I get what you were going for, with placing shapes on the beat for the multiplier. But I feel like... since the controls are click + drag, which tends to be a slower motion, it's really hard to sync that up with fast paced music. On the other hand, a tapping mechanic is much easier to sync up to a steady beat. That's why I found myself tapping the space bar over and over (way more than necessary), to get that multiplier up, and to jam out to the music. Perhaps a tap based control, or slower music, or maybe osu-like motion paths for the dragging could help tie that puzzle/rhythm aspect a little more!
Also in terms of board size, I think a more vertical board would be better suited for this game. Or perhaps a square. Something with shorter rows. I tried to play long enough to get a tetris effect to see what that looked like, but I found that the shape algorithm kept giving me way too many corners for this to be possible. I think letting players have that tetris effect more often could really increase the satisfaction factor and have people playing for even longer.
But of course, all these are just lil suggestions that crossed my mind on how to make this great game even better! :D Well done with the creative ideas and polished gameplay. Best of luck in the jam!
-Sasha