Book of Mercenaries is a single-player game mode first released on April 6, 2021 with new chapters releasing until March 17, 2022. It uses a classic linear adventure format with an appearance similar to Dungeon Run screen. Like Book of Heroes, Book of Mercenaries is about telling the journeys and stories, but the main characters are mercenaries, who were first introduced in Forged in the Barrens as legendary cards and unique to Hearthstone. Like Book of Heroes, Book of Mercenaries featured a chapter for each of the ten classes that existed before Patch 25.0.0.158725, for a total of 80 missions or bosses. It is completely free to play and available to everyone. Additionally, completing a class's story rewards the player a corresponding class pack.