This is cool. It took me a while to figure out which key shrinks you (yes I know it's on the page but sadly no-one reads them - myself also guilty).
Suggestions: UI to show the keys you own.
Bugs: tunnel with the three chests went completely black after I re-entered it a second time (which I guess would be a deal-breaker for that maze), also sometimes I couldn't return to normal size, I couldn't figure out why - in the end I wasn't able grow at all which soft-locked me.