This game's got a solid thought-out core mechanic going for it, and it's very aesthetically pleasing with nice effects and a cold, mellow atmosphere. Where the mechanics don't quite work out though is the way the level design immediately gets carried away blending the puzzles with picky platformer sections with hitboxes and controls/hitboxes that didn't feel fine-tuned for them. It leads to a lot of needless repetition of setting up parts of the same puzzle after dying to a low-hanging spike.
When you add difficulty to a game, be careful to think about what you're making the player repeat when they die and (to a certain degree) if that's a useful thing for them to repeat for them to actually improve where they failed. If your gameplay is centered around the repetition of adding more bodies to a trail and crafting a platforming landscape, it's somewhat counter-productive to start each repetition with a segment that could ruin your run very easily and is unrelated to the goal at hand. It's a jam though, and I get it's super hard to think of ways for every spike and hazard to tie into the challenge of solving the puzzle. BUT, I think a quickfix could've been an undo button for your last death. That cancels out the easy execution mistakes with being able to easily redact them, while keeping the puzzle aspect strong. It also still makes the player retry the challenging parts until they demonstrate the finesse you want, but not having them trudge through steps they've already done many times. Sometimes it's the small features that trim the fat and make a challenge more balanced, so that's probs my advice for next time.
Also I love the ending, it was so extra for a jam game and had such a feeling of celebrating with your little ghostie friends. This game had a lot of effort shine through and I hope I didn't sound too bossy about the nitpicks because I do like it a lot.