Cool idea, I like how the smaller jump you get really helps you feel the weight of the box when you're holding it. In terms of gameplay, I thought the mario-like buttons to switch platforms on/off was satisfying, but I think the controls and game feel could use a bit of work. It was weird to use K to jump and J to pick up, and also I would've really liked some sort of throw trajectory indicator when I was trying to throw the box. Because although pressing W made the box go higher, when I first pressed W, nothing happened on screen, which initially made me think it wouldn't do anything.
I wish I could've got to rate this game during the jam tho, because I love the vibe and the art has a lot of cool polishing touches :)