I should probably make an explanation blogpost of the runes. 🤔
Spoilery responses:
TBH, I've removed the frame-perfect double jump from the upcoming full game (demo still has it!), it was a bit too easy to find accidentally (someone even thought it's a mandatory technique for progressing!), and it also made speedrunning infuriatingly difficult. So it gotta go!
PS. At the moment, the only way to get the butterflies back is to load a save.