objectives are optional but can lead to useful rewards. Once the player has completed a mission on a planet, they can typically return to any previous planet they have visited to attempt missions they could not complete before. In addition to objectives based on platforming and weapon elements, missions may include minigames such as various races and arena combat. Typically, one or two of these minigames must be performed as part of the main story, but further optional challenges can be done to earn greater rewards, typically in the form of "bolts", the unit of currency used throughout the game. There are also missions that focus on Clank, often controlling a set of smaller robots called Gadgebots to travel through areas that Ratchet cannot. Clank's gameplay sections in mainline titles after Tools of Destruction are also considerably more experimental in their gameplay mechanics. In addition to the main gameplay missions, the player can attempt to find special large bolts that are typically hidden or difficult to get to that can be used to upgrade or buy powerful weapons. There are also Skill Points spread throughout the game, which require the player to complete a specific task guided only by the name of the Skill Point. Skill Points are used to unlock extra features such as concept artwork or additional outfits for Ratchet. Each game (excluding Quest for Booty, All 4 One, and Full Frontal Assault) also presents a "Challenge Mode", available after the player has completed the main story; in this mode, the player replays the game, facing more difficult enemies in exchange for a higher bolt payout or more powerful weapon upgrades. Reception Games in the Ratchet & Clank series have been met with mixed to universally acclaimed reviews, with review aggregator scores ranging from 54/100 to 91/100 on Metacritic, and 57% to 92% on GameRankings. The first three games, Ratchet & Clank, Going Commando, and Up Your Arsenal in particular have all been met with critical acclaim. None of the core games in the series (Ratchet & Clank to Deadlocked, the Future series, the PS4 game, and Rift Apart) have been rated below 76/100 on Metacritic. Upon release, the re-imagining of the first game in the series, "Ratchet & Clank (PS4)", quickly became the fastest selling game in the franchise's history. Other media Manga A manga of Ratchet and Clank named was serialized starting in February 2004 in