Very nice and calming puzzle game. I love the idea on how you implemented the jam's theme.
At first i was a bit confused on how exavtly the fusion of the monsters works and initially thought it would be random. Maybe i missed a tutorial text. When i understood that the order was from top to bottom, i realized that this mechanic gives this game a lot of room for new interesting puzzels.
I think you can solve all puzzles in multiple different ways. Which is very nice!
Overall i think this is a pretty good submission. Good work.