Disclaimer: I fully understand this is a game jam game not everything can be done but even then I give very "tough" feedback so if you can't handle that kind of "criticism" it's ok just don't read my message.
First of all it's very unfortunate to see all of the missing features, it happens, just need to be more careful with time usage and not overscoping.
So the music is kind of loud and can get not very tolerable after a lil while, thankfully there's actual volume options but the default can be turned down to 50% instead of being close to 100% in my opinion and also be very careful with using very short loops as the "main background music".
What I would recommend is first adding in those missing features, atleast the main ones as otherwise it can't really be tested properly if you get what I mean and because atleast you are aware of them I won't mention them (but I will still give suggestions on how to improve if I can think of some).
The jump's gravity could be toned down as one falls way too fast and the movement feels quite stiff so be careful with that, try using "tricks" like coyote jump, input buffer and that, they are very important for a good amount of platformers to "feel good to play", obviously do be careful to not end up making the jump a "moon jump" either.
If a life/lives system is to be implemented I recommend when running out of life/lives to reset the level and give endless continues, it all depends if the level structure is gonna stay as it is or its going to be changed.
I'd also recommend any sort of feedback while fixing the furnace with that I mean it's impossible to tell how long it takes to fix it, the most simple might be a bar on top of the furnace to tell how much/long is left to fix it completely.
The snowmen could not just have a vfx but they could also have an animation for shooting too if you were only planning to add vfx as visual cue.
Also UI inside the levels not just for the lifes but could be for example how many snowmen are left (this one is not that necessary unless you plan to make destroying snowmen a possible secondary/main objective in a level, who knows) and how many furnaces are left to fix (this one on the other hand could be nice)
All in all, not bad, you got something submitted and published, that's great. I think this has potential to be it's nice little own arcade game.