This was a pretty nice platformer. I made it to the end despite dying a bunch, which isn't something I can say all the games I played.
I did find this platformer way on the simpler end. The main mechanic—flipping—is fine, and the level design around it is great for how short the game is (though I would have appreciated at least something like moving platforms or a midair gravity switch to spice things up in the second half). I also appreciate that the character flips rather than the rest of the screen; makes things a lot less hard on the eyes. My main qualm is movement itself. It doesn't feel bad—I actually really like the character's movement speed and jump height. However, there's a lot that could be done both mechanically and visually to improve movement.
Instead of the player immediately hitting max speed or stopping, why not have the player accelerate or decelerate. That windup, even if for a tiny fraction of a second, can make movement feel more smooth while keeping things precise. Instead of the player plummeting like a meteor during long falls, why not give the player a max fall speed so the player can more easily follow the character? You could also let the player jump less high by releasing the jump button early, or press down to fastfall if you implement that max fall speed from earlier.
On the aesthetic side of things, there's a lot of juice you could add to movement. Particle effects when the player moves around. A smoother camera that accelerates with the character rather than being glued to them. A walking animation, a jump animation, a landing animation, etc. Some sort of visual effect when the player fits (I like the idea of something similar to the Geometry Dash effect). These would all make movement in this game more satisfying.
Speaking of visuals, I also want to note readability. Most of game elements contrast really well with each other, which is great! It makes it easy to tell what you can and can't land on. The one exception, however, are the spikes on the ground. The dark gray blends in with the ground super easily, so it's very easy to run into spikes without even seeing them. The floating spikes don't have this issue—they're bright as can be—so this could be fixed by recoloring the ground spikes to match them.
But criticisms aside, good stuff! I've been on a hunt for platformers in this jam, and this definitely helped with that itch.