This is a great example of a simple concept that builds upon itself with every level, either increasing the challenge for a specific gameplay mechanic or introducing new ones. Difficulty curve is pretty masterfully executed. While the mechanics aren't anything groundbreaking they're executed well with very competent level design with only a few minor hiccups (3 box towers take way too long to push, can easily get boxes stuck in a corner). If I was being very nitpicky I'd say the jumping mechanics behave differently when pressing a direction and jump simultaneously than when you press them in sequence which can make the platforming fiddly on one or two levels. Music gets repetitive as does the jump sound but honestly that's being very harsh and nothing that couldn't be fixed given a bit more time and polish. Probably one of the best submissions to the Extra Credits Game Jam #4 that I have played in terms of tutorial, level design and expanding on the initial concept.