Two of the fairies decide to accompany her; Cilia the Moon Fairy and Dora the Sun Fairy. They provide the majority of the dialogue within the game and each has her individual temperament, often in contrast to each other. Mi has to choose which fairy to send to speak on her behalf when initiating conversations with NPCs, and they can influence which quests the player is able to take and may even affect the outcome of those quests. Mi's primary goal involves ringing the Six Bells of Fate, a task which falls upon a member of the Sprocket family every six hundred years and is required by prophecy to prevent the destruction of the world. There are numerous side quests as well and most may be completed in multiple ways, awarding the player with different achievements and endings. "Underground" often breaks the fourth wall, with the developer himself making appearances as an NPC and various characters making remarks on common video-game clichés, including the apparent pointlessness of the main quest. In July 2012, Nifflas announced that he was working on "Knytt Underground", and that it is his biggest game yet. It was released on the PlayStation Network for PlayStation 3 and PS Vita in late December 2012, and the console versions include extra content. The game was released on Steam on October 25, 2013. A Wii U version of the game was confirmed in August 2013, and was being ported by Nygren's colleague Mathias Kærlev. The game was released on December 19, 2013 in both North America and Europe. "Underground" was Nifflas' biggest project at the time of its release, encompassing the biggest world and the most characters, sub-quests and secrets of any of his games thus far. Besides Nifflas' own songs, "Knytt Underground" includes music by D Fast, David Kanaga, Fredrik Häthén, LPChip, Jonas Mattebo, Stephen Ascher, Void Pointer, and Yann Van Der Cruyssen. The soundtrack is available as a free download.