The monk's power should be entirely related to the type of alcohol you are able to get your hands on. You use it, then its puts him at a certain strength/hit/dmg+possible status inflict setup for x amount of turns. As such, there should be NPCs that you buy said alcohol. Obviously, the drink the monk should be much more powerful than any normal being can ingest, so the vendor should be a specific brewer who basicly experiments on the monk.
" Here, try this ale, the secret ingredient is gaso.... garlic "
" Oil Slick Ale, 30 atk power, 90% accuracy, strength +15, chance to set opponents on fire "