Gorgeous atmosphere and art. I particularly loved the transform animations, and the attention to detail with the footstep noises changing.
It looks like remappable controls were on your roadmap and just didn’t get done in time, so apologies if this is already stuff you’ve thought about, but I didn’t like 1-2-3 as the buttons for size switching. I think that some way of sizing up/down (perhaps even with W and S, or with keys on the other hand, e.g. J/K/L or arrow keys) would have been more intuitive. I found myself sizing wrong a large percentage of the time.
I think a lot of the jumps were too hard for level 1, but given you only had one level and wanted to show off the different challenges I suspect you are aware. One suggestion I have though is perhaps to give the big guy a very small horizontal boost. The jumps I found the most frustrating were jumps as the big robot where you had to clear a horizontal gap or avoid wires on the edge of a platform and then land on the platform. In my opinion it would feel better if you could land somewhat centrally, but I usually just landed on the platform with a foot in those cases.
Overall a very neat platformer that has a lot of potential!