Thanks again!
I did, except the music. There are a few visual assets that I've made before the jam, like the rotating coins or some VFX (like the small puffs particles when the player lands or slides). I'm also using a personal code library that I expend as I work on game projects, which allowed me to save some time :)
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About game design itself, being a programmer and not a game designer myself, I actually don't really know what advice I could give you haha. I suppose that game designers should play lots of different games, but this is also the case for others game profressions since it's a very generic advice.
Otherwise it seems you're already working on some games and doing game jams, which is great and you should definitely keep it going, personal projects are really what will make you get better and it's also a proof of motivation :)