Most of the levels in Super Mario Galaxy 2 offer a unique task based around its theme, and many focus on dynamic environments that change or alternate between various states. Super Mario Galaxy 2 contains 242 unique Power Stars to collect overall. These levels, containing Green Stars that are hidden or placed in hard-to-reach areas, require intense exploration and precision and may cause instant death if the player fails. When the player collects all 120 Power Stars, 120 Green Star levels are unlocked. (the former being in even-numbered worlds, and the latter being in odd-numbered worlds), which then allows the player to access the next world. The first six worlds end with a boss level in which the object is to defeat Bowser or Bowser Jr.

The game contains forty-nine galaxies allotted among seven different regions in the universe (called 'worlds'), the general difficulty progressively increasing in each world. This is navigated via a mobile planet called Starship Mario that serves as a hub world, which can be visited anytime and is expanded when new abilities or levels are unlocked. The game provides the player access to the game's galaxies through means of a map system similar to that in previous Mario games such as Super Mario World and New Super Mario Bros. The game retains some gameplay mechanics introduced in the original, such as the blue Star Pointer that allows the player to collect Star Bits and shoot them at enemies, levels that restrict movement to a 2D plane, balance ball levels, and gravity-reversing background arrows.

As in the original, the objective of the game is to travel to the various galaxies and collect Power Stars, which are awarded by completing levels and accomplishing tasks and are used to gain access to later levels. The player controls Mario (or later in the game, his brother Luigi, though using him is optional), who has special abilities such as the 'Spin' attack, long jump, wall jumps, and a variety of somersaults. Planets and galaxies each have varying themes, sizes, landscapes, and climates. The gameplay of Super Mario Galaxy 2 is similar to Super Mario Galaxy, with a focus on platforming based on and around 3D planets, grouped into levels known as galaxies. It is frequently considered by critics to be one of the greatest video games of all time and is one of the best-selling games on the Wii with over seven million copies sold worldwide. Upon release, Super Mario Galaxy 2 was met with critical acclaim, and was considered an improvement over its already-lauded predecessor, with its creativity, gameplay and technological improvements over the original receiving high praise, although its high difficulty, in comparison to its predecessor, received some criticism.

Among the new additions are dynamic environments, new power-ups, and the addition of Yoshi. As such, development time expanded to two and a half years. However, it was later decided that the game would be expanded into a fully fleshed-out sequel when the development staff continued to build upon the game with dozens of new ideas. The game was originally planned as an updated version of Super Mario Galaxy, known as Super Mario Galaxy More. Mario must travel across various galaxies to recover the Power Stars in order to travel to the center of the universe and rescue Princess Peach. The story follows Mario as he pursues the Koopa King, Bowser, into outer space, where he has imprisoned Princess Peach and taken control of the universe using Power Stars and Grand Stars. It was first announced at E3 2009 and is the sequel to 2007's Super Mario Galaxy. Super Mario Galaxy 2 is a 2010 platform video game developed and published by Nintendo for the Wii.

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