Wow, very nice stuff here! I thought the concept was a bit cliche but I was surprised at the amount of unique mechanics and puzzles that were derived from it. Once again, everything you'd expect from a Rob1221 game: great concept, great puzzles, intuitive design that subtly teaches you mechanics, great 'gotcha' and 'eureka' moments in the puzzles that make sure you're not just autopiloting but using your noggin, a great variety of mechanics that are paced well to keep the player hooked and increase the difficulty smoothly, and so on and so forth! It took some effort to pull myself away from this!
My only gripe, if you could call it that, is that I felt like the game does have a pretty big difficulty spike early on, particularly with the stacking double jump mechanic. I liked the challenge and felt like you provided enough hints to figure it out, but even with that, it could be quite tricky to pull off at times. I also found it a bit unintuitive in that you needed to have both stacked at the start to pull off the double jump: you couldn't create the stack midjump to double jump off of it even if they aligned perfectly, unfortunately. You also introduced it only for it to disappear from the levels later on, so perhaps that mechanic could've been left till later levels for the player to be more comfortable with a challenge like that. Anyway, great stuff overall!