I don't recall any known games in which slime% is possible.

Me neither, besides this one. Oracle of Ages has some (mostly useless) transformation rings, but none for Zol; Wario Land transformations are more so the stretchy type; and Monster Boy's are all animal themed. I was wondering if you could include Claymates, that game they just added on NSO, but that's kind of stretching it, plus it would just be a speedrun of the intro cutscene.

Ahh, Crusader of Centy, I remember that game! Those poor mons 😢

It's a really interesting game, I know there've been plenty of games with sad stories like that but they're usually traditional RPGs, not Zelda clones. Also the music is incredible.