i think other than the speed change, i think adding more types of obstacles would make the levels a lot more interesting, and if used during the bryce mode, would make it so you wouldn't have to rely and making just more precise versions of the first ten levels
for example, what if there were objects that are also affected by your gravity? it could lead to some interesting puzzles, where you have to control gravity to get a certain block to some area while not dying yourself, or trying to avoid a block that would kill you on contact, or maybe orbs with more ways to move than just back and forth, such as moving in patterns and such
or if you don't wanna add anything new (considering this is only a test), then i would just say decrease the acceleration, and make the levels in bryce mode less cluttered, by removing some of the unnecessary spikes, timed platforms, and orbs, any way to still make it harder than normal mode, but still enjoyable to play
thanks for understanding my problems and criticisms, i hope the bigger game you're working on will be great :3