Definitely feel the game could benefit from chain lift, brake, and booster pieces. Along with that, there's a few situations where it feels like there's a secret solution, but those options never work, such as on the heartline level where it seems just barely not possible to bypass the keys entirely.
There should be a few levels with alternate solutions, rather than what feels like only one option. But, in the case of the heartline level, since it introduces a new technique, the snake should be right up against the cage, so it's clearly impossible to cheese it.
As for Mudskipper, the level. It would benefit from the introduction of the aforementioned boost piece, where you'd get 1 or 2 of them. And for the other levels, there could be ones with keys that only need one collected to open the cage, while having multiple on the map so the player has more options with how they approach the level.
On the prebuilt pieces note. For levels introducing ideas, having prebuilt track that can be removed would be a good way to show players what not to do without outright telling them. An instance of this could be starting off a level with a sharp turn that throws the hapless and helpless rodent to Timbuktu.