Seeing as Blue Mage has a spellbook, it could be neat to have a Mix-based job with some kind of recipe book for different effects.

I figure instead of using potions from your inventory, though, enabling people to just immediately mix items together and make everything on launch, maybe it could involve manipulating some kind of new item drops from mobs. Perhaps something like the seed/dust materials in Octopath, or the items like Beast Liver from Bravely Default.

Given the versatility of Mix, you could have attack themed recipes, ones based around healing and longevity, or ones based around buffing your defenses or stats.