This is great for a first jam submission. Probably way better than my first ever entry, but there are many things that could use improvement. I apologize in advance if I'm sounding critical. I just think feedback is important when you're starting out (none of the comments I saw below are really giving feedback so I'm going to be a bit harsh to compensate). For one the player control is not up to par with a platformer game. It seems like all that you had code wise was velocity.x = whatever movement direction you're pressing while jump was just a flat adding y velocity. What's missing here is stuff you can find if you searched up and looked and other people's character controllers. It's stuff like coyote time, variable jump height, acceleration/deceleration and just stuff to make the platforming actually feel fun. Apart from that, the movement feels very floaty, which could be good in certain games, but I feel detracts from this one by slowing it down immensely. Another thing I noticed was that I kept getting stuck on random tiles for no reason (if this was purposeful it was not a well implemented mechanic as it felt like a glitch, but I assume it was a bug). This is most likely due to there being a weirdly aligned collision box, and since the character is a box, it gets stuck on the smallest edge. My suggestion for this is to make your player's collision a capsule (and also to double check your collision lol). This was you will be able to roll over small pixels of collision that might accidentally get left behind (checking collision of floor though should definitely come first). Those were my gripes with the main movement, and things that I feel you could definitely improve upon if you just knew where to look. Apart from that, I think your main idea was interesting, but implemented in possibly the most tedious way. You play a level, and repeat it while adding stuff to the end of it. That in itself means I would be replaying a high amount of sections over and over again without any change, and you have to wait for narrator every time. The narrator could easily have been speaking in the background while the player got on with the platforming. I see you tried spicing it with the weird effects, but with no way to predict them and use them to your advantage means they chalked up to a "huh what was that" while I continued to jump the same jump for the 5th time. Also if the collision weirdness I mentioned previously was one of these effects, please add more visual indicators. Stuff like screen shake goes a long way for these big moments. If there's no visual feedback to being stopped by an invisible wall (and that wall is bypassed by jumping), it is indistinguishable to bad geometry and feels unfair. Art wise I think you did great. It's a bit simple, but its cohesive, and audio wise, I suggest you look into editing sound effects in a 3rd party software to make them feel like they came from the same game. As of right now, these sound effects feel like they're all from different games and don't mesh together at all.
Overall, I suggest you focus more on the movement of a 2d platformer than you otherwise did. In platformers, it's all about getting to the platforming, and for the character to be enjoyable to control, while also having some sort of interesting mechanic. In this entry, I feel like you worked against yourself here with the way you implemented both the level design and player controller, shafting your ability to make the weird glitches into actual gameplay elements.
I hope this little rant was semi helpful and wont be passed off as the ramblings of a rando online. This was a great first entry to a jam. Congrats on submitting and I'm hopeful to many more after this.