This is a really solid platformer with a simple but very effective take on the jam's theme. Also, I was pleasantly surprised at how much content the game had without feeling too repetitive. It really took the game from being a tech demo to a full-fledged jam game. Great work!
I liked the variety of themes that the levels had, it really helped the game to feel even more expansive. I'm not sure what format your terrain came in, so I'm not sure if this is possible, but I learned the hard way that it's best to let the game engine do all the heavy lifting in terms of configuring tiles. I think the game's overall polish would have been significantly improved if the terrain had corners and edges that were visually different from the rest. I think that could be achieved using terrain sets.
Back to the fundamentals, the first level served as an excellent tutorial that fully and clearly explained all the mechanics. What I really liked, though, was that it was taught by letting the player make mistakes instead of holding the player's hand and telling them what things did. For example, the first time I touched spikes and collected them as gems I had a massive "aha" moment, and I learned a game mechanic without ever being explicitly told it.
One thing I think was underutilized was water. I think it would have been cool if, instead of "voids" or traditional invisible death planes, there could have been a layer of water under each level. That would have helped, because I was surprised sometimes when there was an invisible death barrier.
Sometimes it felt difficult to fit the player in a one-tile-wide space. That could be helped by making the player's actual hitbox even smaller than it is now, but that's just a suggestion. The opposite controls were a nice touch. They added an extra level of challenge to the game while incorporating the theme. It reminded me of what everyone said about my Tether the World...
I only got stuck once, and that was in Level 3 near the beginning with the tight jump after the fall. I actually thought I was doing something wrong, so I skipped the level and came back to it after I had beaten the rest. (And then I got it second try, so maybe it was just my fault).
I do wish that the levels automatically transitioned into each other and had some sort of indication as to which level it was. That would have just made things marginally clearer.
Overall, this was a really cool game! It reminded me of my Scratch days, but more polished. Speaking of Scratch, you have quite a few followers over there, so you might get even more players if you updated your "What I'm Working On" or made an announcement project.
Also, I wish I could rate it on the jam page, but I didn't submit a game to this jam, so I can't. I'd have given it something like this: Overall: 4/5; Fun: 4/5; Innovation: 4/5; Theme: 5/5; Visuals: 2/5; Audio: 3/5.
From one game dev to another, great work, and keep making games!
- Rochester X
(This comment got way out of hand, I hope you don't mind!)