This is such a clean, polished, and thoughtful jam entry. There's the right mix of ridiculousness and brain-torturing puzzles that I really enjoy. I would have loved to see a devlog about what you accomplished during the Marathon Jam specifically, but other than that I really can't think of anything negative/constructive to say about this game. It's well presented and was a fun challenge to try to wrap my head around what each hand could do and what core problem each level presented.
The trickle of new mechanics was well paced, but you probably have room for many more levels in between to really explore the nooks and crannies of what those mechanics can do. In its present state the game is mechanically dense, but not offensively so (in my opinion). It's like a decadent rich chocolate cake of a game. Those that are not puzzle-aficionados might get frustrated around when the skulls are introduced and would benefit from a couple more levels to get the grasp of things.
I had to stop playing because I have to go to work instead of solving puzzles all day. Maybe I'll check in again this evening, I was excited to see where things were headed once the hands started joining together!