I've been glancing back at this topic frequently since its creation. I kept trying to think of things to add, but kept on deciding against it. Welp, here's what I came up with. I used a three tiles for some extended platforms with a little chain bit to help them connect with the longer chain, more-or-less finished up Polana's background tiles, added a one-block-tall version of Firecat's opaque pillar, and, finally, used my remaining three tiles to create something actually new - some little crystal faces. Two sleeping ones, happy and sad, and an awakened version of the happy one. I decided to spend leave the awakened version of the sad one undone because I'm honestly not entirely sure about the eyes - part of me enjoys how horrifyingly disturbing they are, and the other part of me feels that I really ought to make them look a little more expressive, even if it only means widening the eyes by a pixel.
I've also added a screenshot to show how the slanted platforms would work (in case it wasn't clear). I also did a lot of messing around - using the BG tiles in ways I don't think they were originally meant to be used (which, in this situation, looks pretty bad, but that's my fault), showing the differences between the opaque and transparent versions of the pillar, stuff like that. I've also noted that a cave background would be nice, and something to change up that center block tile would be good, too.
On one final note, it seems this tileset has awakened in me the desire to create incredibly non-linear levels, as this is probably the most open-ended screen I've ever made in my life - and I had a lot of fun putting it together! In fact, I enjoy this screen so much, I'll probably end up using it in an actual level! In any case, that's enough text from me.
(P.S. Ego's crystal flowers are awesome but incredibly unruly to get a handle on.)
Edit: Tileset removed, as per the rules.