If you have a chemist, you have all the power you need. Just !Mix up some of these:
Holy Water + Antidote = Samson's Might, gives one target 10 effective levels.
Potion + Dragon Fang = Dragon Power, gives one target 20 effective levels.
Ether + Phoenix Down = Reincarnate, revives and fully heals one ally.
Elixir + Dark Matter = Antilixir, reduce target's HP and MP to 1.
Phoenix Down + Dark Matter = Death Potion, instant kill.
Maiden's Kiss + Holy Water = Blessed Kiss, gives the target Berserk, Haste, and Image.
Holy Water + Dragon Fang = Holy Breath, which casts Holy.
Potion + Ether = X-Potion, fully restores HP.
Phoenix Down + Dragon Fang = Dragon Defense, Shell + Protect on target.
As a boss, he'll be immune to some of those, possibly the instant death ones, but others will work nicely. And those are far from the most ridiculous combos available. And they're all completely undocumented, at least in-game, which does in fact constitute an unforgivable sin. You might want to look into the ones that grant elemental resistance (or was it absorption?) until the end of the battle, or which boost magic damage.