Mallets, also called Hammers, are consumable items that can be used to inflict grievous damage upon foes (equal to level 5 strength, regardless of Pit's own), or free Centurions from their stony prison. Pit can equip and use mallets at any time, provided he's got at least one in stock, and it won't break until it impacts a foe or Centurion. The Harp can be used to turn enemies into mallets, and they're also commonly purchasable in Stores.
A mallet can be purchased for 20 Hearts. An intimidated merchant sells them for 10, and angered one will raise the price to 50.
Hammers are sold for 20 Hearts here unless Pit is buying from a merchant in a Fortress, where they cost 50 instead. Pit is now able to use hammers even when turned into an eggplant which can be helpful fighting off enemies until the player has reached a nurse.