Thanks!
Yeah so the crawl spaces were actually not supposed to be slidable - yet. After you get double jump, the next level I built was a mini-boss fight where you learned the tactics needed to fight the next level baddies - charging minotaurs and priests that threw magic skulls that shrunk you. Defeating them would get you the shrink skull, which could be used to shrink large opponents (like the minotaurs) and give you the Shrink Slide ability, allowing you to get under those. They also allow you to shrink down the big doors, leading to the next level.
Then the next boss could only be hurt when you shrunk them, and defeating that boss got you a skull that allowed you to enlarge things, and gave you Colossal Kick which made you huge as you kicked, and you can take down certain walls. The next set of enemies was going to include something that was small and could only be hit by your hammer when you made them big, and dagger passed over their heads.
I designed the stuff in the levels to allow for the implementation of these things, hoping that I'd get to them and the levels would already be designed and built. Alas, I ran out of time. I'm working on a (very long) post-mortem devlog post about it.