At the moment of writing this, the soundtrack is fully complete. Its Steam page has already been updated to list all of the tracks.
The third and final type of minigame has also been completed. Originally, it was going to be a "spot the differences" type of game, but that idea didn't make use of the physics-based mechanics. After a quick brainstorm panic, I settled on a guessing minigame in which you are given a list of physic properties and have to locate the object that matches them.
And, in case you are thinking that you can just brute-force it, well... the correct object is chosen at random at the start of the minigame. You will need to either think or get incredibly lucky.