Potions

The Potion Seller's potions are potions of immense strength. Indeed, only the strongest creatures alive can handle their power without dying. Even a dragon would perish upon drinking one. Though their power is great, nothing is known about the specifics of the powers the potions grant, only that they are terribly great and certainly dangerous.

The Seller outright refuses to sell to mere humans, so it is unknown who, if anyone, buys them. We can only pray we never have to find out.