I've been playing this game for quite a bit and it's honestly fallen under one of THE best games I've played so far. I hadn't gotten bored once and I don't think I will for a while, and it's got my artistic noggin thinking: How about there's something in the game that has an ability similar to the Illusion Stones, but giving you something new that's unlockable for your character?
What I'm meaning is, let's say you're a race like an Imp for example. Maybe you want something more for your character that could be considered 'unique', per say. What a 'Mutation Canister (OR) Tome of Mutating' could do is give you something that's considered a mutation for your character. Something that wouldn't usually appear in the character creator menu.
For an Imp, it could be something like a centipede tail. For a Kubold, it could be a dragon wing pretending to be a tail. Or maybe, maybe something more.
Or maybe this idea is a little too much and it could just be completely free as supplementary additions to the character creator? Who knows, I'unno. I'd love to see this game adding in more wacky features to the furry fellers, though, since that is one of my most favorite parts about designing a creature.