Split (Reason: item and quest information needs separating)
The Allan Brew is first mentioned by Allan when he pleads the aspiring Dragon Knight to recruit him, he mentions it possesses the power to make one Stronger, Wiser, and Faster. Mindreading him reveals Allan is a liar and has yet honed the ability to brew such a potion.
Upon choosing Allan, he tries to avoid the subject of the Allan Brew by sending the Dragon Knight out to gather rare herbs and multiple items. His brew in the end turned out to be a tremendous success however, to Allan's amazement and bewilderment.
Allan Brew grants the player 36 resistance to every armor rating when drank. It is the strongest Resistance Potion in the game.
Its relatively easy (with careful gear selection and only four +Ranged Armor enchantments, no +Melee/Magic required) to reach a neat 60% to all resistances, and an Allan Brew is just strong enough to push 60% to the perfect cap of 66% while barehanded... the other resistance potions aren't good enough and require sacrificing Lifeline enchantments and such. The result is having the best possible damage resistance no matter the skills or weapons chosen, and it doesn't even require allocating any stat points at all if charms are chosen carefully as well (all need to be at least +4, but that's doable in the expansion).