A solid entry! I was suprised, thought "a classic platformer" and then bam, metroidvania! A really smooth tutorial on how to use your powers (give player a easy level to test them out freely before removing them). I did not finished it, propably that soft lock you are writing about, no way to exit an area, no more upgrades in range.
But it was really fun watching how the main character is growing back with each upgrade, a fun idea :)
I liked both the music and graphics but some sprites were badly readable, I would trade some of visual attractiveness for readability, I could not tell what some of the sprites represent.