Pretty cool demo.
Here's some feedback:
-I would definitely add coyote time, I sometimes pressed jump slightly too late and use double jump instead of jumping.
-Adding drop shadow would help with platforming too.
-Move camera a bit up and make it only move up and down when player moves certain distance up and down
Here's a video talking about it if I explained it poorly.
also I would add reset camera button that would rotate camera to the same rotation player is facing.
-Timer should stop if you finish the timed action, it's kind of annoying to still hear it after you finish.-Also the first time I jumped on the leaf I though it would collapse after a few seconds (It just felt less stable than previous platforms I jumped on.
-I would make the sound of the singing monkeys a bit louder, I didn't realized what the buttons were doing at first. Also I had to go three times to listen to the song before I managed to do it.
-Adding more sound effects like waling, landing etc... would improve the experience.
-Monocle is barely visible and too me way too long to find. I would add it some glow texture behind it or something to make it a bit more visible. Also its a bit weird to having to interact with it to collect it instead just walking into it like rest of collectibles.
-Maybe adding something that indicates to the player that its possible to interact with it would be useful.
-Swimming feels horrible but I don't know if that's intentional or not.
-I collected 10 marmosets. I don't know if that's all of them but I couldn't find any more.
-Also Im a bit disappointed that the blue egg does nothing. I tried interacting with it, attacking it with both attacks, throwing fruit at it and nothing :(
Overall I see potential, Hope my feedback will help you improve you game, good luck on development :)