It's atonishing tht you did all this by yourself. I think is my favourite entry of this jam. The idea of the game is risky and hard to pull it off, but overall I think you did great! Congratulations for your amazing job!
Let me give you some feedback that I think can improve the game:
Overall the controls felt good, I feel like you should freeze the character a couple of frames when he jumps of a wall to avoid pixel perfect inputs from the player. I think a bit of coyote time would help as well. I usually don't play with the keyboard mapping you chose, but I got used to them mid-game, I'd only suggest to use the W key for jumping as well, it was a bit tricky to slide with S and inmediatly afterwards jump with J.
I love the past versions of yourself idea, very reminiscent of Celeste's "Badeline" sections, You really created some interesting situations and presented different challenges. But I think is lacking a sort of trail to know the direction they are coming from, when there are a lot of them is hard to tell. I think you should limit the maximum amount of clones you can have, I was about to defeat the final boss but I couldn't beacuse the level was filled of clones and there was simply not enough space, sometimes I even died inmediatly after respawning in the previous clone hahaha.
I also didn't quite get the jump over your clones mechanic, in the last section before the game . I felt I overcame it by luck more than by skill hahahah I didn't understand at all what was happening, and it's very tricky to pull it off, I think this can be a point where a lot of player can get stuck and frustated and drop the game, be careful with this please :)
I liked a lot the idea of choosing which clone you want to revert when you die, it gives the chance to the player to choose wheter he wants to start from the beginning or just repeat a small section. The only thing that annoyed me about this is that you can respawn in a position where other clones are currently in, and I think abruptly cutting off the music really kills the flow. Personally I'd prefer if you didn't stop the music, maybe add a Low-pass filter or whatever, but something that enhances that fast paced-game idea, This was a noticeable issue in the final boss, it's practically imposible to listen to the whole track without interuptions hahaha.
Speaking about music, I'm surprised that you did it yourself as well. My main issue is that the frequencies were not balanced and the sound was really distorted, you should try to balance it using and equalizer, but overall it fits fine in the game (By the way, if you are planning on continue working on this game I would really like to work on some music if you need/want :D)
Summing up (I wrote a lot, I know xD ), really good work! Interesting mechanics and executions. There are some issued here and there, but I can say without a doubt that this is a very good game. Congrats!