There are two types of Potions that affect the drop rates of cards found in Booster Packs of all Editions: Alchemy and Legendary. Each charge is effective for a single card, and only 1 charge of each potion can be used per card.
Potion charges can be purchased in the POTION SHOP by the individual charge, with Guild and bulk discounts always available.
Alchemy Potion - Use an Alchemy Potion charge to double your chance of that card being a Gold Foil card.
Legendary Potion - Use a Legendary Potion charge to double your chance of that card being a Legendary card.
NOTE: Legendary and Alchemy Potions are only applicable to cards from Booster Packs. They cannot be used on cards found in Loot Chests.